luogu P1127 词链

传送门

典型的建模

对于每个字符串 视为从首字母向尾字母连一条边

跑一下欧拉路即可

Code:

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<cmath>
#include<queue>
#include<vector>
#include<iostream>
#include<iomanip>
#define itn int
#define ms(a,b) memset(a,b,sizeof a)
#define rep(i,a,n) for(int i = a;i <= n;i++)
#define per(i,n,a) for(int i = n;i >= a;i--)
#define inf 2147483647
using namespace std;
typedef long long ll;
ll read() {
    ll as = 0,fu = 1;
    char c = getchar();
    while(c < '0' || c > '9') {
        if(c == '-') fu = -1;
        c = getchar();
    }
    while(c >= '0' && c <= '9') {
        as = as * 10 + c - '0';
        c = getchar();
    }
    return as * fu;
}
//head
const int N = 10006;
int n;
struct line {
    int x,y,l;
    char s[30];
    bool operator < (const line &o) const {
        rep(i,0,min(l-1,o.l-1)) {
            if(s[i] < o.s[i]) return 1;
            if(s[i] > o.s[i]) return 0;
        }
        if(l < o.l) return 1;
        return 0;
    }
    void read() {
        scanf("%s",s);
        l = strlen(s);
        x = s[0] - 'a' + 1,y = s[l-1] - 'a' + 1;
    }
}a[N];
int rdu[30],cdu[30];

bool vis[N];
int stk[N],top;
void dfs(int x) {
    rep(i,1,n) if(a[i].x == x && !vis[i]) {
        vis[i] = 1,dfs(a[i].y),stk[++top] = i;
    }
}
int str;
int main() {
    n = read();
    rep(i,1,n) a[i].read();
    sort(a+1,a+n+1);
    rep(i,1,n) rdu[a[i].y]++,cdu[a[i].x]++;
    
    rep(i,1,26) if(cdu[i] == rdu[i] + 1) str = i;
    if(!str) rep(i,1,26) if(cdu[i]) {str = i;break;}
    
    dfs(str);
    
    if(top < n) puts("***"),exit(0);
    while(top) {
        printf("%s",a[stk[top]].s);
        if(--top) putchar('.');
    }
    return 0;
}