Trie

as known as prefix tree.

Implementation

struct TrieNode {
    TrieNode *next[26] = {};
    int count = 0;
};

class Trie {
private:
    TrieNode root;
    TrieNode* searchToNode(string &prefix) {
        auto node = &root;
        for (char c : prefix) {
            if (!node->next[c - 'a']) return NULL;
            node = node->next[c - 'a'];
        }
        return node;
    }
public:
    void insert(string word) {
        auto node = &root;
        for (char c : word) {
            if (!node->next[c - 'a']) node->next[c - 'a'] = new TrieNode();
            node = node->next[c - 'a'];
        }
        node->count++;
    }

    bool search(string word) {
        auto node = searchToNode(word);
        return node && node->count;
    }

    bool startsWith(string prefix) {
        return searchToNode(prefix);
    }
};

Problems

• 208. Implement Trie (Prefix Tree) (Medium) Direct Implementation

• 212. Word Search II (Hard)

• 745. Prefix and Suffix Search (Hard)

• 839. Similar String Groups (Hard)

• 1032. Stream of Characters (Hard)