为什么零分啊

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
using namespace std;
#include<iostream>
#include<math.h>
#include<algorithm>
int n, m;
char board[1001][1001];
bool come[1001][1001];
long long maax = 0;
void dfs(int y, int x, long long sum)
{
    if (y > n || x > n || y < 1 || x < 1 || come[y][x])
    {
        return;
    }
    come[y][x] = 1;
    char mid = board[y][x];
    int turn = 0;
    if (board[y][x + 1] != mid)
        dfs(y, x + 1, sum + 1);
    else
        turn++;
    if (board[y][x - 1] != mid)
        dfs(y, x - 1, sum + 1);
    else
        turn++;
    if (board[y + 1][x] != mid)
        dfs(y + 1, x, sum + 1);
    else
        turn++;
    if (board[y - 1][x] != mid)
        dfs(y - 1, x, sum + 1);
    else
        turn++;
    maax = max(maax, sum);
    return;

}
int main()
{
    scanf("%d %d", &n, &m);
    getchar();
    for (int i = 1; i <= n; i++)
    {
        for (int t = 1; t <= n; t++)
            scanf("%c", &board[i][t]);
        getchar();
    }
    while (m-- > 0)
    {
        int y, x;
        scanf("%d%d", &y, &x);
        memset(come, 0, sizeof(come));
        dfs(y, x, 1);
        printf("%lld\n", maax);
        maax = 0;
    }
    return 0;
}

明明自己的数据和样例都过了，是我理解错题意了吗