Create implement-trie-prefix-tree.cpp

Author: kamyu104

C++/implement-trie-prefix-tree.cpp

@@ -0,0 +1,66 @@
+// Time:  O(n), per operation
+// Space: O(1)
+
+class TrieNode {
+public:
+    // Initialize your data structure here.
+    TrieNode() : is_string(false) {
+        
+    }
+    bool is_string;
+    unordered_map<char, TrieNode *> leaves;
+};
+
+class Trie {
+public:
+    Trie() {
+        root_ = new TrieNode();
+    }
+
+    // Inserts a word into the trie.
+    void insert(string word) {
+        auto *cur = root_;
+        for (const auto& c : word) {
+            if (!cur->leaves.count(c)) {
+                cur->leaves[c] = new TrieNode();
+            }
+            cur = cur->leaves[c];
+        }
+        cur->is_string = true;
+    }
+
+    // Returns if the word is in the trie.
+    bool search(string word) {
+        auto *node = childSearch(word);
+        if (node) {
+            return node->is_string;
+        }
+        return false;   
+    }
+
+    // Returns if there is any word in the trie
+    // that starts with the given prefix.
+    bool startsWith(string prefix) {
+        return childSearch(prefix);
+    }
+
+    TrieNode * childSearch(const string& word) {
+        auto *cur = root_;
+        for (const auto& c : word) {
+            if (cur->leaves.count(c)) {
+                cur = cur->leaves[c];
+            } else {
+                return nullptr;
+            }
+        }
+        return cur;
+    }
+
+private:
+    TrieNode* root_;
+};
+
+// Your Trie object will be instantiated and called as such:
+// Trie trie;
+// trie.insert("somestring");
+// trie.search("key");