洛谷P1341 无序字母对【欧拉路】【dfs】

 1 #include<cstdio>
 2 #include<cstdlib>
 3 #include<map>
 4 #include<set>
 5 #include<cstring>
 6 #include<algorithm>
 7 #include<vector>
 8 #include<cmath> 
 9 #include<stack>
10 #include<queue>
11 #include<iostream>
12 
13 #define inf 0x7fffffff
14 using namespace std;
15 typedef long long LL;
16 typedef pair<int, int> pr;
17 
18 int n;
19 const int maxm = 3000;
20 const int maxn = 300;
21 int g[maxn][maxn];
22 //int head[maxn], to[maxm * 2], nxt[maxm * 2], vis[maxm * 2];
23 int deg[maxn];
24 int tot = 1;
25 
26 stack<int>ans;
27 
28 void dfs(int now){
29     
30     for(int i = 0; i <= 150; i++){
31         if(g[now][i] <= 0)continue;
32         g[now][i]--;g[i][now]--;
33         dfs(i);
34     }
35     ans.push(now);
36     //printf("%c", now);
37 }
38 
39 int main()
40 {
41     scanf("%d", &n);
42     for(int i = 0; i < n; i++){
43         string s;
44         cin>>s;
45         g[s[0]][s[1]]++;g[s[1]][s[0]]++;
46         //cout<<s[0]-‘A‘<<" "<<s[1]-‘A‘<<endl;
47         deg[s[0]]++;
48         deg[s[1]]++; 
49         //add(s[0] - ‘A‘, s[1] - ‘A‘);
50     }
51     
52     //printf("%d\n", deg[‘I‘ - ‘A‘]);
53     int cnt = 0, dian = 0;
54     for(int i = 0; i <= 150; i++){
55         if(deg[i] % 2){
56             cnt++;
57             if(!dian)dian = i;
58         }
59     }
60     if(!cnt){
61         for(int i = 0; i <= 150; i++){
62             if(deg[i]){
63                 dian = i;
64                 break;
65             }
66         }
67     }
68     
69     if(cnt && cnt != 2){
70         printf("No Solution\n");
71     }
72     else{
73         dfs(dian);
74         //cout<<ans.size()<<endl;
75         if(ans.size() >= n+1){
76             while(!ans.empty()){
77                 printf("%c", ans.top());
78                 ans.pop();
79             }
80             printf("\n");
81         }
82         else{
83             printf("No Solution\n");
84         }
85     }
86     
87 }