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digitspace
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Week 02算法题
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‎Week_02/G20200343030569/LeetCode_105_569.java‎

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public class LeetCode_105_569 {
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public static void main(String[] args) {
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int[] preorder = {3,9,20,15,7};
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int[] inorder = {9,3,15,20,7};
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TreeNode root = new LeetCode_105_569().new Solution().buildTree(preorder, inorder);
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System.out.println( root.val );
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}
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public class TreeNode {
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int val;
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TreeNode left;
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TreeNode right;
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TreeNode(int x) { val = x; }
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}
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class Solution {
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public TreeNode buildTree(int[] preorder, int[] inorder) {
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return recurseBuildTree(preorder, inorder);
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}
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TreeNode recurseBuildTree(int[] preorder, int[] inorder )
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{
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if( preorder.length == 0 )
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return null;
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TreeNode root = new TreeNode(preorder[0]);
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int idx = arraySearch(inorder, preorder[0]);
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root.left = recurseBuildTree(subArray(preorder,1,idx),subArray(inorder,0,idx));
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root.right = recurseBuildTree(subArray(preorder,idx+1,preorder.length-idx-1),subArray(inorder,idx+1,inorder.length-idx-1));
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return root;
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}
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int[] subArray( int[] a, int begin, int length )
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{
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if( a.length < length+begin )
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return new int[0];
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int[] sub = new int[length];
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System.arraycopy(a, begin, sub, 0, length);
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return sub;
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}
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int arraySearch( int[] a, int key ) {
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for ( int i = 0; i < a.length; i++ ) {
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if ( a[i] == key )
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return i;
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}
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return -1;
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}
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}
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}

‎Week_02/G20200343030569/LeetCode_144_569.java‎

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import java.util.LinkedList;
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import java.util.List;
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import java.util.Stack;
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/*
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* 144. Binary Tree Preorder Traversal
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* 二叉树的前序遍历
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*/
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public class LeetCode_144_569 {
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int index;
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TreeNode buildTreeNode(Integer data[]){
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if( index >= data.length )
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return null;
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Integer value = data[index++];
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TreeNode node = null;
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if ( value != null ) {
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node = new TreeNode(value);
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node.left = buildTreeNode(data);
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node.right = buildTreeNode(data);
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}
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return node;
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}
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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//输入: [1,null,2,3]
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Integer[] treeData = { 1, null, 2, 3 };
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LeetCode_144_569 main = new LeetCode_144_569();
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TreeNode node = main.buildTreeNode(treeData);
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List<Integer> result = main.new Solution().preorderTraversal(node);
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for(Integer v: result)
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System.out.println(v);
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}
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public class TreeNode {
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int val;
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TreeNode left;
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TreeNode right;
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TreeNode(int x) { val = x; }
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}
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class Solution {
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public List<Integer> preorderTraversal(TreeNode root) {
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List<Integer> result = new LinkedList<Integer>();
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Stack<TreeNode> stack = new Stack<TreeNode>();
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if ( root == null )
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return result;
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stack.push(root);
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while ( !stack.isEmpty() ) {
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TreeNode node = stack.pop();
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result.add( node.val );
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if ( node.right != null )
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stack.push( node.right );
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if ( node.left != null )
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stack.push( node.left );
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}
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return result;
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}
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}
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}

‎Week_02/G20200343030569/LeetCode_145_569.java‎

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import java.util.LinkedList;
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import java.util.List;
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import java.util.Stack;
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/*
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* 145. Binary Tree Postorder Traversal
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* 二叉树的后序遍历
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*/
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public class LeetCode_145_569 {
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int index;
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TreeNode buildTreeNode(Integer data[]){
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if( index >= data.length )
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return null;
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Integer value = data[index++];
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TreeNode node = null;
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if ( value != null ) {
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node = new TreeNode(value);
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node.left = buildTreeNode(data);
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node.right = buildTreeNode(data);
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}
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return node;
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}
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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//输入: [1,null,2,3]
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Integer[] treeData = { 1, null, 2, 3 };
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LeetCode_145_569 main = new LeetCode_145_569();
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TreeNode node = main.buildTreeNode(treeData);
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List<Integer> result = main.new Solution().postorderTraversal(node);
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for(Integer v: result)
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System.out.println(v);
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}
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public class TreeNode {
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int val;
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TreeNode left;
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TreeNode right;
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TreeNode(int x) { val = x; }
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}
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class Solution {
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public List<Integer> postorderTraversal(TreeNode root) {
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LinkedList<Integer> result = new LinkedList<Integer>();
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Stack<TreeNode> stack = new Stack<TreeNode>();
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if ( root == null )
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return result;
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while ( !stack.isEmpty() || root != null ) {
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if ( root != null ) {
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result.addFirst(root.val);
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stack.push(root);
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root = root.right;
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} else {
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TreeNode node = stack.pop();
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root = node.left;
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}
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}
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return result;
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}
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}
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}

‎Week_02/G20200343030569/LeetCode_236_569.java‎

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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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public class LeetCode_236_569 {
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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LeetCode_236_569 main = new LeetCode_236_569();
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TreeNode result = main.new Solution().lowestCommonAncestor(null, null, null);
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}
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public class TreeNode {
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int val;
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TreeNode left;
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TreeNode right;
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TreeNode(int x) { val = x; }
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}
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class Solution {
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TreeNode ancestor;
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public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
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recurseFind(root, p, q);
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return ancestor;
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}
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int recurseFind(TreeNode node, TreeNode p, TreeNode q) {
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if ( node == null )
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return 0;
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if ( ancestor != null )
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return 0;
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int leftFlag = recurseFind(node.left, p, q);
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int rightFlag = recurseFind(node.right, p, q);
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int pFlag = (node == p || node==q) ? 1 : 0;
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if( leftFlag + rightFlag + pFlag >=2 )
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ancestor = node;
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return (leftFlag + rightFlag + pFlag)>0 ? 1 : 0;
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}
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}
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}

‎Week_02/G20200343030569/LeetCode_429_569.java‎

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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.LinkedList;
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import java.util.List;
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public class LeetCode_429_569 {
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public static void main(String[] args) {
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LeetCode_429_569 main = new LeetCode_429_569();
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Node node1 = main.new Node(1);
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Node node3 = main.new Node(3);
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Node node2 = main.new Node(2);
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Node node4 = main.new Node(4);
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Node node5 = main.new Node(5);
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Node node6 = main.new Node(6);
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node1.children = new ArrayList();
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node1.children.add(node3);
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node1.children.add(node2);
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node1.children.add(node4);
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node3.children = new ArrayList();
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node3.children.add(node5);
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node3.children.add(node6);
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node2.children = new ArrayList();
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node4.children = new ArrayList();
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node5.children = new ArrayList();
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node6.children = new ArrayList();
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List<List<Integer>> result = main.new Solution().levelOrder(node1);
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for(List v: result)
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System.out.println(Arrays.toString(v.toArray()));
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}
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class Node {
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public int val;
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public List<Node> children;
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public Node() {}
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public Node(int _val) {
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val = _val;
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}
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public Node(int _val, List<Node> _children) {
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val = _val;
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children = _children;
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}
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};
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class Solution {
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public List<List<Integer>> levelOrder(Node root) {
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List<List<Integer>> result = new ArrayList<>();
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if (root == null)
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return result;
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List<Node> levelNodes = new LinkedList<Node>();
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levelNodes.add(root);
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while( levelNodes.size() > 0 ) {
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List<Node> nextLevelNodes = new LinkedList<Node>();
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List<Integer> levelValues = new LinkedList<Integer>();
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result.add(levelValues);
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for( Node n : levelNodes ) {
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levelValues.add(n.val);
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for ( Node c : n.children ) {
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nextLevelNodes.add(c);
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}
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}
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levelNodes = nextLevelNodes;
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}
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return result;
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}
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}
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}

‎Week_02/G20200343030569/LeetCode_49_569.java‎

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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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/*
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* 49. Group Anagrams
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* 字母异位词分组
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*/
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public class LeetCode_49_569 {
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public static void main(String[] args) {
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// TODO Auto-generated method stub
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String[] strs = { "eat", "tea", "tan", "ate", "nat", "bat" };
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LeetCode_49_569 main = new LeetCode_49_569();
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List<List<String>> result = main.new Solution().groupAnagrams(strs);
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for ( List<String> group: result ) {
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System.out.println(Arrays.toString(group.toArray()));
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}
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}
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class Solution {
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public List<List<String>> groupAnagrams(String[] strs) {
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Map<String, List> anaMap = new HashMap<String, List>();
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for ( String s: strs ) {
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char[] t = s.toCharArray();
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Arrays.sort(t);
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String key = new String(t);
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if ( !anaMap.containsKey(key) ) {
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anaMap.put(key, new ArrayList() );
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}
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anaMap.get(key).add(s);
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}
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return new ArrayList( anaMap.values() );
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}
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}
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}

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