POJ 3494 Largest Submatrix of All 1’s

POJ 2796 Feel Good

HDU 1506 Largest Rectangle in a Histogram

和这两题一样的方法。

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;

const int maxn=+;
int a[maxn];
int L[maxn],R[maxn];
int m,n;
int tmp[maxn][maxn],b[maxn][maxn];

void f()
{
    for(int i=; i<=n; i++) L[i]=i;
    for(int i=; i<=n; i++)
    {
        if(a[i]>a[i-]) continue;
        int pre=L[i-];
        while()
        {
            L[i]=pre;
            if(pre==||a[pre-]<a[i]) break;
            pre=L[pre-];
        }
    }

    for(int i=n; i>=; i--) R[i]=i;
    for(int i=n-; i>=; i--)
    {
        if(a[i]>a[i+]) continue;
        int pre=R[i+];
        while()
        {
            R[i]=pre;
            if(pre==n||a[pre+]<a[i]) break;
            pre=R[pre+];
        }
    }

}

int main()
{
    while(~scanf("%d%d",&n,&m))
    {
        memset(b,,sizeof b);
        for(int i=; i<=n; i++)
            for(int j=; j<=m; j++) scanf("%d",&tmp[i][j]);

        for(int i=; i<=n; i++)
            for(int j=; j<=m; j++)
            {
                if(tmp[i][j]==) continue;
                b[i][j]=b[i][j-]+tmp[i][j];
            }

        int ans=;
        for(int j=;j<=m;j++)
        {
            for(int i=;i<=n;i++) a[i]=b[i][j];
            f();
            for(int i=;i<=n;i++) ans=max(ans,a[i]*(R[i]-L[i]+));
        }
        printf("%d\n",ans);
    }
    return ;
}