悬线法

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利用极大化思想。
UVA 1330
AC Code:

#include<bits/stdc++.h>
#define maxn 1005
using namespace std;

int n,m,u[maxn][maxn],l[maxn][maxn],r[maxn][maxn];
bool is[maxn][maxn];
char s[3];

int main()
{
    int T;
    for(scanf("%d",&T);T--;)
    {
        scanf("%d%d",&n,&m);
        memset(u,0,sizeof u);
        memset(l,0,sizeof l);
        memset(r,0,sizeof r);
        for(int i=1;i<=n;i++)
            for(int j=1;j<=m;j++)
            {
                scanf("%s",s);
                if(is[i][j] = (s[0]=='R'))
                    u[i][j] = 0;
                else
                    if(i) u[i][j] = 1 + u[i-1][j];
                    else  u[i][j] = 1;
                l[i][j] = j+1;
                r[i][j] = j-1;
            }
        for(int i=1;i<=n;i++) l[i][0] = 1 , r[i][m+1] = m;

        for(int i=1;i<=n;i++)
            for(int j=1;j<=m;j++)
                if(!is[i][j]) l[i][j] = l[i][j-1];

        for(int i=1;i<=n;i++)
            for(int j=m;j>=1;j--)
                if(!is[i][j]) r[i][j] = r[i][j+1];

        int ans=0;
        for(int i=1;i<=n;i++)
            for(int j=1;j<=m;j++)
            {
                if(i>1 && !is[i-1][j] && !is[i][j]) l[i][j] = max(l[i][j] , l[i-1][j]) , r[i][j] = min(r[i][j] , r[i-1][j]);
                if(!is[i][j])ans = max(ans , (r[i][j] - l[i][j] + 1) * u[i][j]);
            }
        printf("%d\n",ans*3);
    }
}