暴力求后缀最值，为什么吸氧能过但不吸氧70pts

#include <iostream>
using namespace std;
typedef long long ll;

const int N = 1010;
int a, b, n;
ll mat[N][N], ans = 1e9, minn[2][N][N], maxn[2][N][N];

int main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cin >> a >> b >> n;
    for (int i = 1; i <= a; ++i)
        for (int j = 1; j <= b; ++j) cin >> mat[i][j];

    // 求最小值    
    for (int i = 1; i <= a; ++i)
        for (int j = 1; j + n - 1 <= b; ++j) {
            minn[0][i][j] = 1e9;
            for (int k = j; k <= j + n - 1; ++k)
                minn[0][i][j] = min(minn[0][i][j], mat[i][k]);
        }
    for (int j = 1; j <= b; ++j)
        for (int i = 1; i + n - 1 <= a; ++i) {
            minn[1][i][j] = 1e9;
            for (int k = i; k <= i + n - 1; ++k)
                minn[1][i][j] = min(minn[1][i][j], minn[0][k][j]);
        }
    
    // 求最大值
    for (int i = 1; i <= a; ++i)
        for (int j = 1; j + n - 1 <= b; ++j)
            for (int k = j; k <= j + n - 1; ++k)
                maxn[0][i][j] = max(maxn[0][i][j], mat[i][k]);
    for (int j = 1; j <= b; ++j)
        for (int i = 1; i + n - 1 <= a; ++i)
            for (int k = i; k <= i + n - 1; ++k)
                maxn[1][i][j] = max(maxn[1][i][j], maxn[0][k][j]);

    // 求差
    for (int i = 1; i <= a - n + 1; ++i)
        for (int j = 1; j <= b - n + 1; ++j)
            ans = min(ans, maxn[1][i][j] - minn[1][i][j]);
    cout << ans << '\n';
    return 0;
}