[luoguP1169] [ZJOI2007]棋盘制作（单调栈）

传送门

和玉蟾宫差不多

——代码

#include <cstdio>
#include <iostream>

using namespace std;

const int MAXN = 2001;
int n, m, ans1, ans2, top;
int a[MAXN][MAXN][2], s[MAXN], r[MAXN], l[MAXN];

inline void work(int k)
{
    int i, j;
    for(i = 0; i <= 1; i++)
    {
        a[k][0][i] = a[k][m + 1][i] = -1;
        top = 0;
        for(j = 1; j <= m + 1; j++)
        {
            while(top && a[k][s[top]][i] > a[k][j][i]) r[s[top--]] = j;
            s[++top] = j;
        }
        top = 0;
        for(j = m; j >= 0; j--)
        {
            while(top && a[k][s[top]][i] > a[k][j][i]) l[s[top--]] = j;
            s[++top] = j;
        }
        for(j = 1; j <= m; j++)
        {
            ans1 = max(ans1, min(a[k][j][i], r[j] - l[j] - 1) * min(a[k][j][i], r[j] - l[j] - 1));
            ans2 = max(ans2, a[k][j][i] * (r[j] - l[j] - 1));
        }
    }
}

int main()
{
    int i, j, x;
    scanf("%d %d", &n, &m);
    for(i = 1; i <= n; i++)
        for(j = 1; j <= m; j++)
        {
            scanf("%d", &x);
            if((i + j) % 2) x ^= 1;
            a[i][j][x] = a[i - 1][j][x] + 1;
        }
    for(i = 1; i <= n; i++) work(i);
    printf("%d
%d
", ans1, ans2);
    return 0;
}