The Kingdom of JOIOI (JOI17_joioi)

#include <bits/stdc++.h>
using namespace std;

const int N = 2005;
const int inf = 1e9 + 7;

int n, m;
int a[N][N], tmp[N][N];
int mnR[N][N], mxR[N][N];
int pos[N];

void _rotate() {
    for (int i = 1; i <= n; ++i) for (int j = 1; j <= m; ++j) tmp[j][n + 1 - i] = a[i][j];
    swap(n, m);
    for (int i = 1; i <= n; ++i) for (int j = 1; j <= m; ++j) a[i][j] = tmp[i][j];
}

int ans = inf;
int mn = inf;

bool check(int val) {
    for (int i = 1; i <= n; ++i) {
        pos[i] = m + 1;
        for (int j = 1; j <= m; ++j) if (a[i][j] > mn + val) { pos[i] = j; break; }
    }

    for (int i = 1; i <= n; ++i) {
        mnR[i][m + 1] = inf; mxR[i][m + 1] = 0;
        for (int j = m; j >= 1; --j) {
            mnR[i][j] = min(mnR[i][j + 1], a[i][j]);
            mxR[i][j] = max(mxR[i][j + 1], a[i][j]);
        }
    }

    int cur = m;
    int cur_min = inf, cur_max = 0;
    for (int i = 1; i <= n; ++i) {
        cur = min(cur, pos[i] - 1);
        cur_min = min(cur_min, mnR[i][cur + 1]);
        cur_max = max(cur_max, mxR[i][cur + 1]);
    }

    return cur_max - cur_min <= val;
}

void solve() {
    int l = 0, r = inf;
    while(l < r) {
        int mid = ((l + r) >> 1);
        if (check(mid)) r = mid; else l = mid + 1;
    }
    if (check(l)) ans = min(ans, l);
}

int main() {
    ios_base::sync_with_stdio(false); cin.tie(0);
    cin >> n >> m;
    for (int i = 1; i <= n; ++i) {
        for (int j = 1; j <= m; ++j) cin >> a[i][j], mn = min(mn, a[i][j]);
    }

    solve();

    _rotate();
    solve();

    _rotate();
    solve();

    _rotate();
    solve();

    printf("%d\n", ans);
}