题目：208. 实现 Trie (前缀树)

思路：经典的字典树题型，（Tire模板题）acwing 835. Trie字符串统计

C++版本：

class Trie {
public:
    static const int N=1e6+5;
    int p[N][30];
    int ans[N];
    int idx=0;

    Trie() {
        memset(p,0,sizeof p);
        memset(ans,0,sizeof ans);
    }
    
    void insert(string word) {
        int t=0;
        for(auto x:word){
            if(p[t][x-'a']==0){
                p[t][x-'a']=++idx;
            }
            t=p[t][x-'a'];
        }
        ans[t]++;
    }
    
    bool search(string word) {
        bool flag=1;
        int t=0;
        for(auto x:word){
            if(p[t][x-'a']==0){
                flag=0;
                break;
            }
            t=p[t][x-'a'];
        }
        return flag&&ans[t];
    }
    
    bool startsWith(string prefix) {
        bool flag=1;
        int t=0;
        for(auto x:prefix){
            if(p[t][x-'a']==0){
                flag=0;
                break;
            }
            t=p[t][x-'a'];
        }
        return flag;
    }
};

/**
 * Your Trie object will be instantiated and called as such:
 * Trie* obj = new Trie();
 * obj->insert(word);
 * bool param_2 = obj->search(word);
 * bool param_3 = obj->startsWith(prefix);
 */

JAVA版本：

class Trie {
    private static final int N=100005;
    int[][] p;
    int[] ans;
    int idx;

    public Trie() {
        p=new int[N][30];
        ans=new int[N];
        idx=0;
    }
    
    public void insert(String word) {
        int t=0;
        for(int i=0;i<word.length();i++){
            char x=word.charAt(i);
            if(p[t][x-'a']==0){
                p[t][x-'a']=++idx;
            }
            t=p[t][x-'a'];
        }
        ans[t]++;
    }
    
    public boolean search(String word) {
        boolean flag=true;
        int t=0;
        for(int i=0;i<word.length();i++){
            char x=word.charAt(i);
            if(p[t][x-'a']==0){
                flag=false;
                break;
            }
            t=p[t][x-'a'];
        }
        return flag&&ans[t]!=0;
    }
    
    public boolean startsWith(String prefix) {
        boolean flag=true;
        int t=0;
        for(int i=0;i<prefix.length();i++){
            char x=prefix.charAt(i);
            if(p[t][x-'a']==0){
                flag=false;
                break;
            }
            t=p[t][x-'a'];
        }
        return flag;
    }
}

/**
 * Your Trie object will be instantiated and called as such:
 * Trie obj = new Trie();
 * obj.insert(word);
 * boolean param_2 = obj.search(word);
 * boolean param_3 = obj.startsWith(prefix);
 */