十月例题F题

F - City Game

Time Limit:3000MS     Memory Limit:0KB     64bit IO Format:%lld & %llu

Bob is a strategy game programming specialist. In his new city building game the gaming environment
is as follows: a city is built up by areas, in which there are streets, trees, factories and buildings. There
is still some space in the area that is unoccupied. The strategic task of his game is to win as much
rent money from these free spaces. To win rent money you must erect buildings, that can only be
rectangular, as long and wide as you can. Bob is trying to find a way to build the biggest possible
building in each area. But he comes across some problems — he is not allowed to destroy already
existing buildings, trees, factories and streets in the area he is building in.
Each area has its width and length. The area is divided into a grid of equal square units. The rent
paid for each unit on which you’re building stands is 3$.
Your task is to help Bob solve this problem. The whole city is divided into K areas. Each one of
the areas is rectangular and has a different grid size with its own length M and width N. The existing
occupied units are marked with the symbol ‘R’. The unoccupied units are marked with the symbol ‘F’.
Input
The first line of the input file contains an integer K — determining the number of datasets. Next lines
contain the area descriptions. One description is defined in the following way: The first line contains
two integers-area length M ≤ 1000 and width N ≤ 1000, separated by a blank space. The next M
lines contain N symbols that mark the reserved or free grid units, separated by a blank space. The
symbols used are:
R - reserved unit
F - free unit
In the end of each area description there is a separating line.
Output
For each data set in the input file print on a separate line, on the standard output, the integer that
represents the profit obtained by erecting the largest building in the area encoded by the data set.
Sample Input
2
5 6
R F F F F F
F F F F F F
R R R F F F
F F F F F F
F F F F F F
5 5
R R R R R
R R R R R
R R R R R
R R R R R
R R R R R
Sample Output
45
0

题解:给定一个m*n的矩阵，其中一些格子是空地（F），其他障碍是（R），找到一个全部由F组成的面积最大的子矩阵，输出其面积乘3的结果

大致思路，扫描法，扫描他的运动极限。

#include<stdio.h>
#include<string.h>
int main()
{
    char s[2];
    int l[1001],r[1001],d[2][1001];
    int i,j,n,m,t,max,res;
    scanf("%d",&t);
    while(t--)
    {
        memset(d,0,sizeof(d));
        scanf("%d%d",&n,&m);
        res=0;
        for(i=1;i<=n;i++)
        {
            for(j=1;j<=m;j++)
            {
                scanf("%s",s);
                if(s[0]=='F')
                    d[i%2][j]=d[(i-1)%2][j]+1;    //滚动数组
                else
                    d[i%2][j]=0;
                l[j]=r[j]=j;
            }
            for(j=2;j<=m;j++)
            {
                while(l[j]>1&&d[i%2][l[j]-1]>=d[i%2][j])
                    l[j]=l[l[j]-1];
            }  //向左延伸
            for(j=m-1;j>=1;j--)
            {
                while(r[j]<m&&d[i%2][r[j]+1]>=d[i%2][j])
                    r[j]=r[r[j]+1];
            }  //向右延伸
            max=0;
            for(j=1;j<=m;j++)
                if((r[j]-l[j]+1)*d[i%2][j]>max)
                    max=(r[j]-l[j]+1)*d[i%2][j];
            if(max>res)
                res=max;
        }
        printf("%d
",res*3);
    }
    return 0;
}