Largest Submatrix of All 1’s（单调栈）

Description
Given a m-by-n (0,1)-matrix, of all its submatrices of all 1’s which is the largest? By largest we mean that the submatrix has the most elements.

Input
The input contains multiple test cases. Each test case begins with m and n (1 ≤ m, n ≤ 2000) on line. Then come the elements of a (0,1)-matrix in row-major order on m lines each with n numbers. The input ends once EOF is met.

Output
For each test case, output one line containing the number of elements of the largest submatrix of all 1’s. If the given matrix is of all 0’s, output 0.

Sample Input
2 2
0 0
0 0
4 4
0 0 0 0
0 1 1 0
0 1 1 0
0 0 0 0

Sample Output
0
4

Source
POJ Founder Monthly Contest – 2008.01.31, xfxyjwf

思路
将每一行的矩阵视为其在该层的高度，对矩阵进行初始化，
例
0 1 0 1 0
0 0 1 1 1
0 1 1 0 1
可化为
0 1 0 1 0
0 0 1 2 1
0 1 2 0 2
即可通过单调栈推出每层矩阵的最大面积

代码实现

#include
#include
#include
#include


using namespace std;
typedef long long ll;
const int N=2005;
int n,m;
int h[N],s[N];
stackl;
int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        int ans=0;
        memset(h,0,sizeof(h));
        for(int i=0;is[j])
                    {
                        top=l.top();
                        ans=max(ans,(j-top)*s[top]);
                        l.pop();
                    }
                    l.push(top);
                    s[top]=s[j];
                }
            }
        }
        printf("%d\n",ans);
    }
    return 0;
}