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\n",ans);

    }

}

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