Trie

字典树

class Trie {
    public:
        Trie() {
            root = new Node();
        }

        ~Trie() {
            destroy(root);
        }

        void insert(string word) {
            Node* next = root;
            for (int i = 0; i < word.length(); ++i) {
                if (next->next[word[i] - 'a'] == NULL) {
                    next->next[word[i] - 'a'] = new Node();
                }
                next = next->next[word[i] - 'a'];            
            }
            next->val++; // 只要最尾个字符的位置计数
        }

        int search(string word) {
            Node* next = root;
            int i = 0;
            for (; i < word.length() && next != NULL; ++i) {
                next = next->next[word[i] - 'a'];
            }
            if (i == word.length() && next != NULL) {
                return next->val;
            } else {
                return 0;
            }    
        }

    private:
        struct Node {
            int val;
            Node *next[26];
            Node(): val(0) {
                memset(next, 0, sizeof(Node*) * 26);
            }
        };

        void destroy(Node* p) {
            if (p == NULL) return;
            for (int i = 0; i < 26; ++i) {
                destroy(p->next[i]);
            }
            delete p;
        }
        Node* root;    
};