省委代码：

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>
#define maxn 100
#define maxm 10000using namespace std;struct edge{int next,to;
}e[maxm];int point[maxn],cnt;
int l,r,q[maxn],in[maxn];
char s[110][110];void addedge(int x,int y)
{e[++cnt].next=point[x];e[cnt].to=y;point[x]=cnt;
}void toposort()
{l=r=0;for(int i=0;i<26;i++)if(in[i]==0)q[++r]=i;while(l<r){int x=q[++l];for(int i=point[x];i;i=e[i].next){int y=e[i].to;in[y]--;if(in[y]==0)q[++r]=y;}}
}int main()
{scanf("%d",&n);for(int i=1;i<=n;i++)scanf("%s",s[i]);for(int i=1;i<n;i++){int len1=strlen(s[i]);int len2=strlen(s[i+1]);bool flag=0;for(int j=0;j<min(len1,len2);j++)if(s[i][j]==s[i+1][j])continue;else{flag=1;in[s[i+1][j]-'a']++;addedge(s[i][j]-'a',s[i+1][j]-'a');break;}if(flag==0 && len2<len1){printf("Impossible");return 0;}}toposort();if(l<26)printf("Impossible");elsefor(int i=1;i<=26;i++)printf("%c",q[i]+'a');return 0;
}

转载于:https://www.cnblogs.com/ShineEternal/p/11221382.html

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CF510C Fox And Names——拓扑排序练习

省委代码：

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