单词拼接传送门
//单词拼接
#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;
struct node
{
char s[31];
int first, last;
};
node a[1001];
int degree_in[1001], degree_out[1001], m, order[1001];
bool used[1001];
int f()
{
int x1, x2, ans = 0, i;
x1 = x2 = 0;
for (i = 0; i < 26; ++i)
{
if (abs(degree_in[i] - degree_out[i]) >= 2)
return -1;
else if (degree_in[i] - degree_out[i] == 1)
x1++;
else if (degree_in[i] - degree_out[i] == -1)
{
x2++;
ans = i;
}
}
if (x1>1 || x2 > 1) //当时三个度时,必定是 12 和21,相同的不能大于等于2,不然不能构成欧拉回路
return -1;
else if (x1 == 0)
{
for (i = 0; i < 26; ++i)
if (degree_out[i])
return i; //找到一个就行
}
else
return ans;
}
bool cmp(node a, node b)
{
return strcmp(a.s, b.s) < 0;
}
bool dfs(int st, int cnt)
{
int i;
if (cnt == m)
return 1;
for (i = 0; i < m; ++i)
{
if (a[i].first < st || used[i])
continue;
else if (a[i].first > st)
return false;
used[i] = true;
order[cnt] = i;
if (dfs(a[i].last, cnt + 1))
return 1;
used[i] = false;//回溯判断是否形成欧拉路径
}
return false;
}
int main()
{
int N, len, i, start;
scanf("%d", &N);
while (N--)
{
memset(used, false, sizeof(used));
memset(degree_out, 0, sizeof(degree_out));
memset(degree_in, 0, sizeof(degree_in));
scanf("%d", &m);
for (i = 0; i < m; ++i)
{
scanf("%s", a[i].s);
len = strlen(a[i].s);
a[i].first = a[i].s[0] - 'a';
a[i].last = a[i].s[len - 1] - 'a';
degree_out[a[i].s[0] - 'a']++;
degree_in[a[i].s[len - 1] - 'a']++;//注意这里的入肚出度
}
start = f();
if (start == -1)
{
printf("***\n");
continue;
}
sort(a, a + m, cmp);
if (!dfs(start, 0))
{
printf("***\n");
continue;
}
printf("%s", a[order[0]].s);
for (i = 1; i < m; i++)
printf(".%s", a[order[i]].s);
printf("\n");
}
return 0;
}
![](https://img2018.cnblogs.com/blog/1239274/201811/1239274-20181130225828686-817213536.jpg)