hdu 1251 统计难题

点击打开链接hdu 1251

题意：给点一序列的字符串，再给你一些单词，问以这个单词为前缀的字符串的个数，注意本身也是自己的前缀

思路：把给定的字符串建立一棵字典树，每一个节点保存的是当前节点为结尾的字符串出现的次数，那么对于给定的单词我们只要去查找字典树即可

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
using namespace std;

const int MAXN = 1000010;
const int N = 26;

struct Node{
    int cnt;
    Node* child[N]; 
};
Node node[MAXN];
Node* root;
int pos;

Node* newNode(){
    node[pos].cnt = 0;
    for(int i = 0 ; i < N ; i++)
        node[pos].child[i] = NULL;
    return &node[pos++];
}

void insert(char* str){
    int len = strlen(str);
    Node* s = root;
    for(int i = 0 ; i < len ; i++){
        int num = str[i]-'a';
        if(s->child[num] == NULL)
            s->child[num] = newNode();
        s = s->child[num];
        s->cnt++;
    }
}

int search(char* str){
    int len = strlen(str);
    Node* s = root;
    for(int i = 0 ; i < len ; i++){
        int num = str[i]-'a';
        if(s->child[num] == NULL)
            return 0;
        s = s->child[num];
    }
    return s->cnt;
}

int main(){
    pos = 0;
    root = newNode();
    char str[N];
    while(gets(str) && str[0] != '\0')
        insert(str); 
    while(scanf("%s" , str) != EOF)
        printf("%d\n" , search(str));
    return 0;
}