poj 1094 Sorting It All Out

每输入一个关系拓扑排序一次

注意当有多种情况的时候 要判断是否已经有环， 有环则直接Sorted sequence cannot be determined.

 

判断是否有环很多方法，我用的是传递闭包判断map[i][i]是否为1  为1则有环

#include<stdio.h>#include<string.h>const int MAXN = 27;int n, m, cnt;int in[MAXN], map[MAXN][MAXN];bool finish, more;char sort[MAXN];bool floyed(){int nmap[MAXN][MAXN];memcpy(nmap, map, sizeof(map));for(int k = 0; k < n; ++k)for(int i = 0; i < n; ++i)for(int j = 0; j < n; ++j){if(nmap[i][k] && nmap[k][j])nmap[i][j] = 1;}for(int i = 0; i < n; ++i)if(nmap[i][i])return true;return false;}void toposort(){int z, znum = 0;int st[MAXN], top = -1;more = false;cnt = 0;memset(in, 0, sizeof(in));for(int i = 0; i < n; ++i)for(int j = 0; j < n; ++j)if(map[i][j])in[j]++;for(int i = 0; i < n; ++i){if(in[i] == 0){z = i;znum++;}}if(znum > 1){more = true;return;}st[++top] = z;while(top != -1){int tmp = st[top--];sort[cnt++] = (char)(tmp + 'A');if(top >= 0){more = true;break;}for(int i = 0; i < n; ++i){if(map[tmp][i]){in[i]--;if(in[i] == 0)st[++top] = i;}}}sort[cnt] = '/0';}int main(){char s[4];while(scanf("%d%d",&n, &m) == 2, n + m){memset(map, 0, sizeof(map));finish = false;for(int i = 1; i <= m; ++i){scanf("%s",s);map[s[0] - 'A'][s[2] - 'A'] = 1;if(!finish){if(floyed()){printf("Inconsistency found after %d relations./n",i);finish = true;continue;} toposort();if(!more){printf("Sorted sequence determined after %d relations: %s./n",i, sort);finish = true;}}}if(!finish)printf("Sorted sequence cannot be determined./n");}return 0;}