USACO算法系列四十——frameup

    题目：http://www.nocow.cn/index.php/Translate:USACO/frameup

    第一次理解这道题目的时候理解错了。这句话很关键：“矩形的每条边中，至少有一部分是可见的。注意，一个角同时属于两条边。”

    也就是说每条边至少有一个点是可见的，这样我们就可以确定出矩形的边框。

    这样就可以确定出整个矩形，然后利用深度遍历的方法，搜索出所有的答案。

    代码如下：

#include <iostream>#include <fstream>#define SIZE 31using namespace std;ifstream fin("frameup.in");ofstream fout("frameup.out");struct Rect {int sx;int sy;int ex;int ey;Rect(){sx = SIZE;sy = SIZE;ex = 0;ey = 0;}};int h, w;char pic[SIZE][SIZE];int use[26] = {0};Rect rect[26];int direct[4] = {0};int result[26]={0};int rl =0;bool isUse(char c){int index = c - 'A';if (use[index] == 0){return false;}return true;}//是否是矩形bool isRect(int index){char c = index + 'A';//左边的竖线for (int i=rect[index].sx; i <= rect[index].ex; i ++){if (pic[i][rect[index].sy] != c && isUse(pic[i][rect[index].sy])){return false;}}//上边的线for(int i=rect[index].sy; i <= rect[index].ey; i ++)/{if (pic[rect[index].sx][i] != c && isUse(pic[rect[index].sx][i])){return false;}}//下边的线for(int i=rect[index].sy; i <= rect[index].ey; i ++)/{if (pic[rect[index].ex][i] != c && isUse(pic[rect[index].ex][i])){return false;}}//右边的线for (int i=rect[index].sx; i <= rect[index].ex; i ++){if (pic[i][rect[index].ey] != c && isUse(pic[i][rect[index].ey])){return false;}}return true;}void DFS(int step){if (step == rl){for (int i=step-1; i >= 0; i --){char c = 'A' + result[i];fout<<c;}fout <<endl;}else{for (int i=0; i < 26; i ++){if (use[i] == 1){if (isRect(i)){use[i] = 0;result[step] = i;DFS(step+1);use[i] = 1;}}//end if}//end for}}//读取数据void init(){fin >> h >> w;for(int i=1; i <= h; i ++){for ( int j=1; j <= w; j ++){fin >> pic[i][j];if (pic[i][j] != '.'){int index = pic[i][j] - 'A';if (use[index] ==0){rl ++;use[index] = 1;}if (rect[index].sx > i){rect[index].sx = i;}if (rect[index].sy > j){rect[index].sy = j;}if (rect[index].ex < i){rect[index].ex = i;}if (rect[index].ey < j){rect[index].ey = j;}}///end if pic}//end for j}//end for i}int main(){init();DFS(0);return 0;}