POJ--1128--Frame Stacking【拓扑排序】

来源：互联网发布：windows update更新慢编辑：程序博客网时间：2024/06/12 21:03

链接：http://poj.org/problem?id=1128

题意：有几张图片，给你叠加到一起之后的图，问叠加的可能性，如有多种可能则按字典序由小到大输出。

思路：根据给出的图形建一个图，被覆盖的图片向覆盖它的图片建边，然后拓扑排序。

拓扑排序按照字母顺序从小到大找入度为0的点，用dfs形式的拓扑排序，就按照字典序输出了。

POJ1270的做法也类似：代码

#include<cstring>#include<string>#include<fstream>#include<iostream>#include<iomanip>#include<cstdio>#include<cctype>#include<algorithm>#include<queue>#include<deque>#include<map>#include<set>#include<vector>#include<stack>#include<ctime>#include<cstdlib>#include<functional>#include<cmath>using namespace std;#define PI acos(-1.0)#define MAXN 35#define eps 1e-7#define INF 0x3F3F3F3F      //0x7FFFFFFF#define LLINF 0x7FFFFFFFFFFFFFFF#define seed 1313131#define MOD 1000000007#define ll long long#define ull unsigned ll#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1struct node{    int x, y;}left_top[MAXN], right_bottom[MAXN];int n, m, tot;int edge[MAXN][MAXN], in[MAXN];char mapp[MAXN][MAXN];char str[MAXN];int vis[MAXN];void dfs(int len){    int i, j;    if(len == tot){        puts(str);        return ;    }    for(i = 0; i < 26; i++){        if(!vis[i]) continue;        if(in[i] == 0){            in[i] = -1;            str[len] = i + 'A';            for(j = 0; j < 26; j++){                if(edge[i][j]) in[j]--;            }            dfs(len + 1);            for(j = 0; j < 26; j++){                if(edge[i][j])  in[j]++;            }            in[i] = 0;        }    }}int main(){    int i, j, k;    while(scanf("%d%d", &n, &m) != EOF){        memset(edge, 0, sizeof(edge));        memset(in, 0, sizeof(in));        memset(vis, 0, sizeof(vis));        memset(str, 0, sizeof(str));        for(i = 0; i < MAXN; i++){            left_top[i].x = left_top[i].y = INF;            right_bottom[i].x = right_bottom[i].y = 0;        }        for(i = 0; i < n; i++)  scanf("%s", mapp[i]);        for(i = 0; i < n; i++){            for(j = 0; j < m; j++){                if(mapp[i][j] == '.')   continue;                int temp = mapp[i][j] - 'A';                if(left_top[temp].x > i)    left_top[temp].x = i;                if(left_top[temp].y > j)    left_top[temp].y = j;                if(right_bottom[temp].x < i)    right_bottom[temp].x = i;                if(right_bottom[temp].y < j)    right_bottom[temp].y = j;            }        }        tot = 0;        for(i = 0; i < 26; i++){            if(left_top[i].x == INF)    continue;            tot++;            vis[i] = 1;            for(j = left_top[i].x; j <= right_bottom[i].x; j++){                if(mapp[j][left_top[i].y] != i + 'A')   edge[i][mapp[j][left_top[i].y] - 'A'] = 1;                if(mapp[j][right_bottom[i].y] != i + 'A')   edge[i][mapp[j][right_bottom[i].y] - 'A'] = 1;            }            for(j = left_top[i].y + 1; j <= right_bottom[i].y - 1; j++){                if(mapp[left_top[i].x][j] != i + 'A')   edge[i][mapp[left_top[i].x][j] - 'A'] = 1;                if(mapp[right_bottom[i].x][j] != i + 'A')   edge[i][mapp[right_bottom[i].x][j] - 'A'] = 1;            }        }        for(i = 0; i < MAXN; i++){            for(j = 0; j < MAXN; j++){                if(edge[i][j])  in[j]++;            }        }        dfs(0);    }    return 0;}

0 0