hdu2870（dp求最大子矩阵）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=2870

分析：分别转换成'a','b','c'三种来求，其实就跟hdu1505一样了。。。

#include <cstdio>
#include <cstring>
#include <cmath>
#include <iostream>
#include <algorithm>
#include <queue>
#include <cstdlib>
#include <vector>
#include <set>
#include <map>
#define LL long long
#define inf 1<<30
using namespace std;
char s[1010][1010],str[1010][1010];
int sum[1005][1005],l[1010],r[1010];
int n,m;
int solve(char ch,char a,char b,char c)
{
    int t;
    memset(sum,0,sizeof(sum));
    for(int i=1; i<=n; i++)
        for(int j=1; j<=m; j++)
        {
            if(s[i][j]==a||s[i][j]==b||s[i][j]==c)str[i][j]=ch;
            else str[i][j]=s[i][j];
        }
    for(int i=1; i<=n; i++)
        for(int j=1; j<=m; j++)
        {

            if(str[i][j]==ch)sum[i][j]=sum[i-1][j]+1;
            else sum[i][j]=0;
        }
    int ans=-1;
    for(int i=1; i<=n; i++)
    {
        l[1]=1;
        r[m]=m;
        for(int j=2; j<=m; j++)
        {
            t=j;
            while(t>1&&sum[i][j]<=sum[i][t-1])t=l[t-1];
            l[j]=t;
        }
        for(int j=m-1; j>=1; j--)
        {
            t=j;
            while(t<m&&sum[i][j]<=sum[i][t+1])t=r[t+1];
            r[j]=t;
        }
        for(int j=1; j<=m; j++)
            ans=max(ans,(r[j]-l[j]+1)*sum[i][j]);
    }
    return ans;
}
int main()
{
    while(scanf("%d%d",&n,&m)>0)
    {
        for(int i=1;i<=n;i++)scanf("%s",s[i]+1);
        int ans=-1;
        ans=max(ans,solve('a','w','y','z'));
        ans=max(ans,solve('b','w','x','z'));
        ans=max(ans,solve('c','x','y','z'));
        printf("%d
",ans);
    }
}