hdu1045 Fire Net（DFS枚举）

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <time.h>
#include <string>
#include <map>
#include <stack>
#include <vector>
#include <set>
#include <queue>
#define M  10000
#define maxn (4 + 2)
#define pi acos(-1.0)
using namespace std;
char a[maxn][maxn];
int n,maxs = -1;
void Shoot(int t)   //假如a[t/n][t%n]放上机枪，那么把它能扫射的区域标记为‘D‘(Die),机枪的位置标记为‘!‘;
{
    int x = t / n;
    int y = t % n;
    a[x][y] = ‘!‘;
    for(int i = x + 1; i < n; i ++)
    {
        if(a[i][y] == ‘.‘)      a[i][y] = ‘D‘;
        else if(a[i][y] == ‘X‘) break;
        else if(a[i][y] != ‘!‘) a[i][y] ++;
    }
    for(int i = x - 1; i >= 0; i --)
    {
        if(a[i][y] == ‘.‘)      a[i][y] = ‘D‘;
        else if(a[i][y] == ‘X‘) break;
        else if(a[i][y] != ‘!‘) a[i][y] ++;
    }
    for(int i = y + 1; i < n; i ++)
    {
        if(a[x][i] == ‘.‘)      a[x][i] = ‘D‘;
        else if(a[x][i] == ‘X‘) break;
        else if(a[x][i] != ‘!‘) a[x][i] ++;
    }
    for(int i = y - 1; i >= 0; i --)
    {
        if(a[x][i] == ‘.‘)      a[x][i] = ‘D‘;
        else if(a[x][i] == ‘X‘) break;
        else if(a[x][i] != ‘!‘) a[x][i] ++;
    }
}
void Live(int t)        //假如a[t/n][t%n]不放机枪，那么逆转上面的函数;
{
    int x = t / n;
    int y = t % n;
    a[x][y] = ‘.‘;
    for(int i = x + 1; i < n; i ++)
    {
        if(a[i][y] == ‘X‘)       break;
        else if(a[i][y] == ‘D‘)  a[i][y] = ‘.‘;
        else if(a[i][y] == ‘E‘)  a[i][y] = ‘D‘;
    }
    for(int i = x - 1; i >= 0; i --)
    {
        if(a[i][y] == ‘X‘)       break;
        else if(a[i][y] == ‘D‘)  a[i][y] = ‘.‘;
        else if(a[i][y] == ‘E‘)  a[i][y] = ‘D‘;
    }
    for(int i = y + 1; i < n; i ++)
    {
        if(a[x][i] == ‘X‘)       break;
        else if(a[x][i] == ‘D‘)  a[x][i] = ‘.‘;
        else if(a[x][i] == ‘E‘)  a[x][i] = ‘D‘;
    }
    for(int i = y - 1; i >= 0; i --)
    {
        if(a[x][i] == ‘X‘)       break;
        else if(a[x][i] == ‘D‘)  a[x][i] = ‘.‘;
        else if(a[x][i] == ‘E‘)  a[x][i] = ‘D‘;
    }
}
void Dfs(int t)     //用DFS搜索，
{
    if(t >= n * n)  //到达分支的结尾时候，查找一共有多少机枪
    {
        int cnt = 0;
        for(int i = 0; i < n; i ++)
            for(int j = 0; j < n; j ++)
                if(a[i][j] == ‘!‘)  cnt ++;
        maxs = max(maxs,cnt);
        return;
    }
    if(a[t / n][t % n] != ‘.‘)  Dfs(t + 1); //如果这个位置不能放机枪，就到下一位置
    else
    {
        Shoot(t);                           //此地放上机枪
        Dfs(t + 1);
        Live(t);                            //此地不放机枪
        Dfs(t + 1);
    }
}
int main()
{
//    freopen("in.txt","r",stdin);
//    freopen("out.txt","w",stdout);
    while(scanf("%d",&n) && n)
    {
        maxs = -1;
        for(int i = 0; i < n; i ++)            scanf("%s",a[i]);
        Dfs(0);
        printf("%d\n",maxs);
    }
    return 0;
}