洛谷数据 WA #7，云斗 AC

请问是哪里错了？能不能给个hack数据？

#include <string>
#include <cstdio>
#include <algorithm>
using namespace std;

const int MAXN = 3010;

int n, m;
string raw[MAXN], arr[MAXN];

char buf[MAXN];
bool charCmp(char a, char b)
{
    return a > b;
}

int main()
{
    scanf("%d %d", &n, &m);
    for (int i = 1; i <= n; i++)
    {
        scanf("%s", buf);
        raw[i] = string(buf);
        sort(buf, buf + m, charCmp);
        arr[i] = string(buf);
    }
    string m = arr[1];
    for (int i = 1; i <= n; i++)
        m = min(m, arr[i]);
    for (int i = 1; i <= n; i++)
    {
        string s = raw[i];
        sort(s.begin(), s.end());
        if (s <= m)
            printf("1");
        else
            printf("0");
    }
    printf("\n");
    return 0;
}