洛谷 P4147 玉蟾宫 （最大子矩形问题）

这道题用到了悬线法，非常牛逼，可以看这个论文。

https://blog.csdn.net/twtsa/article/details/8120269

#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define REP(i, a, b) for(int i = (a); i < (b); i++)
#define _for(i, a, b) for(int i = (a); i <= (b); i++)
using namespace std;
 
const int MAXN = 2123;
int l[MAXN][MAXN], r[MAXN][MAXN], h[MAXN][MAXN];
int a[MAXN][MAXN], n, m;
 
int main()
{
	scanf("%d%d", &n, &m);
	_for(i, 1, n)
		_for(j, 1, m)
		{
			char c; cin >> c;
			a[i][j] = (c == 'F');
			h[i][j] = 1;
			l[i][j] = r[i][j] = j;
		}
	
	_for(i, 1, n)
	{
		_for(j, 2, m)
			if(a[i][j-1] && a[i][j])
				l[i][j] = l[i][j-1];
		for(int j = m - 1; j >= 1; j--)
			if(a[i][j+1] && a[i][j])
				r[i][j] = r[i][j+1];
	}
	
	int ans = 0;
	_for(i, 1, n)
		_for(j, 1, m)
		{
			if(i > 1 && a[i][j] && a[i-1][j])
			{
				h[i][j] = h[i-1][j] + 1;
				l[i][j] = max(l[i][j], l[i-1][j]);
				r[i][j] = min(r[i][j], r[i-1][j]);
			}
			ans = max(ans, (r[i][j] - l[i][j] + 1) * h[i][j]);
		}
	printf("%d
", 3 * ans);
 
    return 0;
}