208. Implement Trie (Prefix Tree) 💫

README.md

@@ -111,8 +111,9 @@ continually updating 😃.
 * [111. Minimum Depth of Binary Tree](src/0111_minimum_depth_of_binary_tree/minimum_depth_of_binary_tree.go)   *`binary tree;`*   *`dfs`*
 * [112. Path Sum](src/0112_path_sum/path_sum.go)   *`binary tree;`*   *`dfs`*
 * [144. Binary Tree Preorder Traversal](src/0144_binary_tree_preorder_traversal/binary_tree_preorder_traversal.go)   *`binary tree;`*   *`pre-order traversal`*
-* [226. Invert Binary Tree](src/0226_invert_binary_tree/invert_binary_tree.go)   *`binary tree;`*
-* [235. Lowest Common Ancestor of a Binary Search Tree](src/0235_lowest_common_ancestor_of_a_binary_search_tree/lcaoabst.go)   *`binary tree;`*
+* [208. Implement Trie (Prefix Tree)](src/0208_implement_trie_prefix_tree/impltrie.go)   *`trie`*
+* [226. Invert Binary Tree](src/0226_invert_binary_tree/invert_binary_tree.go)   *`binary tree`*
+* [235. Lowest Common Ancestor of a Binary Search Tree](src/0235_lowest_common_ancestor_of_a_binary_search_tree/lcaoabst.go)   *`binary tree`*
 * [257. Binary Tree Paths](src/0257_binary_tree_paths/binary_tree_paths.go)   *`binary tree`*
 * [307. Range Sum Query - Mutable](src/0307_Range_Sum_Query_Mutable/range_sum_query_mut.go)   *`segment tree`*
 * [404. Sum of Left Leaves](src/0404_sum_of_left_leaves/sum_of_left_leaves.go)   *`binary tree`*

src/0208_implement_trie_prefix_tree/impltrie.go

@@ -0,0 +1,72 @@
+/*
+208. Implement Trie (Prefix Tree)
+https://leetcode.com/problems/implement-trie-prefix-tree/
+
+Implement a trie with insert, search, and startsWith methods.
+
+Note:
+You may assume that all inputs are consist of lowercase letters a-z.
+All inputs are guaranteed to be non-empty strings.
+*/
+// time: 2019-01-31
+
+package impltree
+
+type node struct {
+	isWord bool
+	next   map[byte]*node
+}
+
+// Trie prefix tree
+type Trie struct {
+	root *node
+	size int
+}
+
+// Constructor initialize data structure here.
+func Constructor() Trie {
+	return Trie{root: &node{next: make(map[byte]*node)}}
+}
+
+// Insert inserts a word into the trie.
+func (trie *Trie) Insert(word string) {
+	cur := trie.root
+
+	for i := 0; i < len(word); i++ {
+		if _, ok := cur.next[word[i]]; !ok {
+			cur.next[word[i]] = &node{next: make(map[byte]*node)}
+		}
+		cur, _ = cur.next[word[i]]
+	}
+	if !cur.isWord {
+		cur.isWord = true
+		trie.size++
+	}
+}
+
+// Search returns if the word is the trie.
+func (trie *Trie) Search(word string) bool {
+	cur := trie.root
+
+	for i := 0; i < len(word); i++ {
+		if _, ok := cur.next[word[i]]; !ok {
+			return false
+		}
+		cur, _ = cur.next[word[i]]
+	}
+
+	return cur.isWord
+}
+
+// StartsWith returns if there is any word in the trie that starts with the given prefix.
+func (trie *Trie) StartsWith(prefix string) bool {
+	cur := trie.root
+
+	for i := 0; i < len(prefix); i++ {
+		if _, ok := cur.next[prefix[i]]; !ok {
+			return false
+		}
+		cur, _ = cur.next[prefix[i]]
+	}
+	return true
+}

src/0208_implement_trie_prefix_tree/impltrie_test.go

@@ -0,0 +1,25 @@
+package impltree
+
+import "testing"
+
+func TestImplTrie(t *testing.T) {
+	trie := Constructor()
+	trie.Insert("apple")
+
+	for i, j := range map[string]bool{"apple": true, "app": false, "hello": false} {
+		if res := trie.Search(i); res != j {
+			t.Errorf("expected %t, got %t", j, res)
+		}
+	}
+
+	for i, j := range map[string]bool{"app": true, "as": false} {
+		if res := trie.StartsWith(i); res != j {
+			t.Errorf("expected %t, got %t", j, res)
+		}
+	}
+
+	trie.Insert("app")
+	if res := trie.Search("app"); res != true {
+		t.Errorf("expected %t, got %t", true, res)
+	}
+}

src/README.md

@@ -68,6 +68,7 @@
 |0200|[200. Number of Islands](0200_number_of_island/number_of_island.go)|Medium|*`dfs;`* *`bfs`*|
 |0203|[203. Remove Linked List Elements](0203_remove_linked_list_elements/remove_linked_list_elements.go)|Easy|*`linked list`*|
 |0206|[206. Reverse Linked List](0206_reverse_linked_list/reverse_linked_list.go)|Easy|*`linked list`*|
+|0208|[208. Implement Trie (Prefix Tree)](0208_implement_trie_prefix_tree/impltrie.go)|Medium|*`trie`*|
 |0209|[Minimum Size Subarray Sum](./0209_minimum_size_subarray_sum/minimum_size_subarray_sum.go)|Medium|*`sliding window`*|
 |0215|[215. Kth Largest Element in an Array](0215_kth_largest_element_in_an_array/kthleiaa.go)|Medium|*`sort`*|
 |0217|[217. Contains Duplicate](0217_contains_duplicate/contains_duplicate.go)|Easy|*`map`*|