codeforces 510c Fox And Names 拓扑排序

#include <cstdio>#include <cstring>#include <iostream>#include <queue>using namespace std;int t;int ma[30][30];char a[105][105];void tpusort(){int d[30];queue<int> que;queue<int> ans;int dd = 0;for(int i = 0;i < 26;i++){int cc = 0;for(int j = 0;j < 26;j++){cc += ma[j][i];}d[i] = cc;if(cc == 0){que.push(i);}}while(!que.empty()){int tm = que.front();que.pop();ans.push(tm);for(int i = 0;i < 26;i++){if(ma[tm][i] == 1){ma[tm][i] = 0;d[i]--;if(d[i] == 0){que.push(i);}}}}if(ans.size() == 26){while(!ans.empty()){int tm = ans.front();ans.pop();putchar(tm+'a');}printf("\n");}else{printf("Impossible\n");}}int main(){scanf("%d",&t);memset(ma,0,sizeof(ma));for(int i = 0;i < t;i++){scanf("%s",a[i]);}int flag = 1;for(int i = 0;i < t;i++){for(int j = 0;j < i;j++){for(int k = 0;a[j][k];k++){if(a[i][k] == '\0'){flag = 0;break;}if(a[i][k] != a[j][k]){ma[a[j][k]-'a'][a[i][k]-'a'] = 1;break;}}}}if(flag){tpusort();}else{printf("Impossible\n");}return 0;}