add Trie

README.md

@@ -285,8 +285,9 @@ If a problem is too easy to solve, we'll mark it as **straightforward** in order
 * [RBT](./C13-Red-Black-Trees/rbtree.cpp)
 * [Btree](./C18-B-Trees/btree.cpp)
 * [BinomialHeap](./C19-Binomial-Heaps/BinomialHeap.h)  [Driver](././C19-Binomial-Heaps/Main.cpp)
-* [UnionFind](./C21-Data-Structures-for-Disjoint-Sets/uf.cpp)
 * [SegmentTree](./other/segmentTree.cpp)
+* [Trie](./other/trie.cpp)
+* [UnionFind](./C21-Data-Structures-for-Disjoint-Sets/uf.cpp)
 
 ### DYNAMIC/GREEDY
 * [Matrix Chain](./C15-Dynamic-Programming/Matrix-chain-multiplication.c)

other/trie.cpp

@@ -0,0 +1,59 @@
+struct TrieNode {
+    TrieNode *nodes[26];
+    bool word;
+    // Initialize your data structure here.
+    TrieNode(): word(false) {
+        memset(nodes, 0, sizeof(nodes));
+    }
+};
+
+class Trie {
+
+public:
+    Trie() {
+        root = new TrieNode();
+    }
+
+    // Inserts a word into the trie.
+    void insert(const string& s) {
+        TrieNode *tmp = root;
+        for(char ch : s) {
+            int index = ch - 'a';
+            if(tmp->nodes[index] == nullptr) {
+                tmp->nodes[index] = new TrieNode();
+            }
+            tmp = tmp->nodes[index];
+        }
+        tmp->word = true;
+    }
+
+    // Returns if the word is in the trie.
+    bool search(const string& key) const {
+        TrieNode *tmp = root;
+        for(char ch : key) {
+            int index = ch - 'a';
+            if(tmp->nodes[index] == nullptr) {
+                return false;
+            }
+            tmp = tmp->nodes[index];
+        }
+        return tmp->word;
+    }
+
+    // Returns if there is any word in the trie
+    // that starts with the given prefix.
+    bool startsWith(const string& prefix) const {
+        TrieNode *tmp = root;
+        for(char ch : prefix) {
+            int index = ch - 'a';
+            if(tmp->nodes[index] == nullptr) {
+                return false;
+            }
+            tmp = tmp->nodes[index];
+        }
+        return true;
+    }
+
+private:
+    TrieNode* root;
+};