Merge pull request neetcode-gh#84 from Pegasus02K/patch-9

Create 208-Implement-Trie.cpp

Author: neetcode-gh

cpp/208-Implement-Trie.cpp

@@ -0,0 +1,60 @@
+struct TrieNode {
+	TrieNode* children[26];
+	bool isWordEnd;
+
+	TrieNode() : isWordEnd(false) {
+		for (int i = 0; i < 26; ++i)
+			children[i] = nullptr;
+	}
+};
+
+class Trie {
+private:
+	TrieNode* root;
+public:
+	Trie() {
+		root = new TrieNode;
+	}
+
+	void insert(string word) {
+		TrieNode* cur = root;
+
+		int idx;
+		for (int i = 0; i < word.size(); ++i) {
+			idx = word[i] - 'a';
+			if (cur->children[idx] == nullptr)
+				cur->children[idx] = new TrieNode;
+			cur = cur->children[idx];
+		}
+		// mark the last node as end of a word
+		cur->isWordEnd = true;
+	}
+
+	bool search(string word) {
+		TrieNode* cur = root;
+
+		int idx;
+		for (int i = 0; i < word.size(); ++i) {
+			idx = word[i] - 'a';
+			if (cur->children[idx] == nullptr)
+				return false;
+			cur = cur->children[idx];
+		}
+		// check if the node is end of any word
+		return cur->isWordEnd;
+	}
+
+	bool startsWith(string prefix) {
+		TrieNode* cur = root;
+
+		int idx;
+		for (int i = 0; i < prefix.size(); ++i) {
+			idx = prefix[i] - 'a';
+			if (cur->children[idx] == nullptr)
+				return false;
+			cur = cur->children[idx];
+		}
+		// only need to check if the node exists
+		return true;
+	}
+};