51Nod 1127 最短的包含字符串 (尺取法)

#include <iostream>
#include <algorithm>
#include <string>
#include <cstring>

#define INF 0xfffffff
using namespace std;
const int maxn = 26;
int a[maxn];

bool is_ok(){
    for (int i = 0; i < 26; i++){
        if (!a[i])
            return false;
    }
    return true;
}

int main(){
    ios::sync_with_stdio(false);
    string s;
    cin >> s;
    memset(a, 0, sizeof(a));
    bool flag = true;
    a[s[0] - 'A']++;
    int ans = INF;
    int l = 0;
    for (int i = 1; i < s.length(); i++){
        a[s[i] - 'A']++;
        while (is_ok())
        {
            ans = min(ans, i - l + 1);
            a[s[l++] - 'A']--;
        }
    }
    if (ans == INF){
        cout << "No Solution" << endl;
    }
    else
        cout << ans << endl;
    system("pause");
    return 0;
}