单调栈

单调栈

单调栈，就是维护一个栈，使栈中的数据大小呈现(单调递增/单调递减)。

问题描述

给定一个n行m列的矩阵，求该矩阵的最大面积子矩阵。

#include<iostream>
#include<cmath>
#include<algorithm>
#include<stack>
#include<string>
using namespace std;

int t, n, m;
int map[2003][2003], a[2003][2003];
int main()
{
	cin >> t;
	while (t--)
	{
		cin >> n >> m;
		memset(a, 0, sizeof(a));
		for (int i = 0; i < n; i++)
			for (int j = 0; j < m; j++)
				cin >> map[i][j];
		for (int j = 0; j < m; j++)
			a[0][j] = 1;
		for (int j = 0; j < m; j++)
			for (int i = 1; i < n; i++)
				if (map[i][j] >= map[i - 1][j])
					a[i][j] = a[i - 1][j] + 1;
				else
					a[i][j] = 1;
		int ans = m, top;
		stack<int> s;
		for (int i = 1; i < n; i++)
		{
			for (int j = 0; j <= m; j++)
			{
				if (s.empty() || a[i][j] >= a[i][s.top()])
					s.push(j);
				else
				{
					while (!s.empty() && a[i][j] < a[i][s.top()])
					{
						top = s.top();
						s.pop();
						ans = max((j - top) * a[i][top], ans);
					}
					s.push(top);
					a[i][top] = a[i][j];
				}
			}
			s.pop();
		}
		cout << ans << endl;
		for (int i = 0; i < n; i++)
		{
			for (int j = 0; j < m; j++)
				cout << a[i][j] << " ";
			cout << endl;
		}
	}
	return 0;
}