tree problems added.

Author: harshsavasil

binary-tree/center-of-a-tree.py

@@ -0,0 +1,43 @@
+from queue import Queue
+
+# Refer the below link for problem.
+# https://www.youtube.com/watch?v=nzF_9bjDzdc&list=PLDV1Zeh2NRsDfGc8rbQ0_58oEZQVtvoIc&index=4
+
+
+def getCentreOfTree(tree):
+    leaves = []
+    degree = {}
+    for node in tree:
+        degree[node] = len(tree[node])
+        if degree[node] <= 1:  # nodes with degree = 0, 1
+            leaves.append(node)
+    count = len(leaves)
+    n = len(tree)
+    while count < n:
+        new_leaves = []
+        for node in leaves:
+            for neighbor in tree[node]:
+                degree[neighbor] -= 1
+                if degree[neighbor] == 1:
+                    new_leaves.append(neighbor)
+            degree[node] = 0
+        count += len(new_leaves)
+        leaves = new_leaves
+    return leaves
+
+
+if __name__ == '__main__':
+    # undirected graph with no cycles therefore a tree
+    tree = {
+        0: [1],
+        1: [0, 3, 4],
+        2: [3],
+        3: [1, 2, 6, 7],
+        4: [1, 5, 8],
+        5: [4],
+        6: [3, 9],
+        7: [3],
+        8: [4],
+        9:  [6]
+    }
+    print(getCentreOfTree(tree))

binary-tree/height-of-binary-tree.py

@@ -0,0 +1,32 @@
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+
+class Solution:
+    def getHeight(self, root: TreeNode) -> int:
+        if root is None:
+            return -1
+        if root.left is None and root.right is None:  # leaf node
+            return 0
+        return max(self.getHeight(root.left), self.getHeight(root.right)) + 1
+
+
+root = TreeNode(3)
+root.left = TreeNode(5)
+root.left.left = TreeNode(6)
+root.left.right = TreeNode(2)
+root.left.right.left = TreeNode(7)
+root.left.right.right = TreeNode(4)
+root.right = TreeNode(1)
+root.right.left = TreeNode(0)
+root.right.right = TreeNode(8)
+
+
+solution = Solution()
+assert solution.getHeight(root) == 3, "test case 1 failed"
+assert solution.getHeight(root.right) == 1, "test case 1 failed"
+assert solution.getHeight(root.left) == 2, "test case 1 failed"

binary-tree/leaf-node-sum.py

@@ -0,0 +1,36 @@
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+
+class Solution:
+    def getLeafNodeSum(self, root: TreeNode) -> int:
+        if root is None:
+            return 0
+        if root.left is None and root.right is None:
+            return root.val
+        total = 0
+        if root.left:
+            total += self.getLeafNodeSum(root.left)
+        if root.right:
+            total += self.getLeafNodeSum(root.right)
+        return total
+
+
+root = TreeNode(3)
+root.left = TreeNode(5)
+root.left.left = TreeNode(6)
+root.left.right = TreeNode(2)
+root.left.right.left = TreeNode(7)
+root.left.right.right = TreeNode(4)
+root.right = TreeNode(1)
+root.right.left = TreeNode(0)
+root.right.right = TreeNode(8)
+
+
+solution = Solution()
+output = solution.getLeafNodeSum(root)
+assert output == 25, "test case 1 failed"

binary-tree/tree-encoding.py

@@ -0,0 +1,35 @@
+from queue import Queue
+
+# Refer the below link for problem.
+# https://www.youtube.com/watch?v=nzF_9bjDzdc&list=PLDV1Zeh2NRsDfGc8rbQ0_58oEZQVtvoIc&index=4
+
+
+def dfs(node, tree):
+    if node is None:
+        return ""
+    encoding = '0'
+    for child in tree[node]:
+        childEncoding = dfs(child, tree)
+        encoding += childEncoding
+    encoding += '1'
+    return encoding
+
+
+def getEncoding(root, tree):
+    """
+    Perform a dfs and append 0 as you enter a node and 1 when you leave the node.
+    """
+    return dfs(root, tree)
+
+
+if __name__ == '__main__':
+    # undirected graph with no cycles therefore a tree
+    tree = {
+        0: [],
+        1: [0, 2],
+        2: [],
+        3: [5],
+        4: [1, 3],
+        5: []
+    }
+    print(getEncoding(4, tree))