题目链接：http://poj.org/problem?id=2230
题目：
题意：给你m条路径，求一条路径使得从1出发最后回到1，并满足每条路径都恰好被沿着正反两个方向经过一次。
思路：由于可以回到起点，并且题目保证有解，所以本题是欧拉回路。输出路径有两种方法，一种是递归实现，一种是用栈处理，不过两种速度差了1s，不知道是不是我递归没处理好~
代码实现如下（第一种为栈输出路径，对应797ms，第二种为递归，对应1782ms):
1 #include <set> 2 #include <map> 3 #include <queue> 4 #include <stack> 5 #include <cmath> 6 #include <bitset> 7 #include <cstdio> 8 #include <string> 9 #include <vector> 10 #include <cstdlib> 11 #include <cstring> 12 #include <iostream> 13 #include <algorithm> 14 using namespace std; 15 16 typedef long long ll; 17 typedef pair<ll, ll> pll; 18 typedef pair<ll, int> pli; 19 typedef pair<int, ll> pil;; 20 typedef pair<int, int> pii; 21 typedef unsigned long long ull; 22 23 #define lson i<<1 24 #define rson i<<1|1 25 #define bug printf("********* "); 26 #define FIN freopen("D://code//in.txt", "r", stdin); 27 #define debug(x) cout<<"["<<x<<"]" <<endl; 28 #define IO ios::sync_with_stdio(false),cin.tie(0); 29 30 const double eps = 1e-8; 31 const int mod = 10007; 32 const int maxn = 5e4 + 7; 33 const double pi = acos(-1); 34 const int inf = 0x3f3f3f3f; 35 const ll INF = 0x3f3f3f3f3f3f3f; 36 37 int n, m, u, v, tot, top, t; 38 int head[maxn], stc[maxn*10], ans[maxn*10], vis[maxn*10]; 39 40 struct edge { 41 int v, next; 42 }ed[maxn*10]; 43 44 void addedge(int u, int v) { 45 ed[tot].v = v; 46 ed[tot].next = head[u]; 47 head[u] = tot++; 48 ed[tot].v = u; 49 ed[tot].next = head[v]; 50 head[v] = tot++; 51 } 52 53 void eulergraph() { 54 stc[++top] = 1; 55 while(top > 0) { 56 int x = stc[top], i = head[x]; 57 while(i != -1 && vis[i]) i = ed[i].next; 58 if(i != -1) { 59 stc[++top] = ed[i].v; 60 head[x] = ed[i].next; 61 vis[i] = 1; 62 } else { 63 top--; 64 ans[++t] = x; 65 } 66 } 67 } 68 69 int main() { 70 //FIN; 71 scanf("%d%d", &n, &m); 72 tot = top = t = 0; 73 memset(stc, 0, sizeof(stc)); 74 memset(ans, 0, sizeof(ans)); 75 memset(vis, 0, sizeof(vis)); 76 memset(head, -1, sizeof(head)); 77 for(int i = 1; i <= m; i++) { 78 scanf("%d%d", &u, &v); 79 addedge(u, v); 80 } 81 eulergraph(); 82 for(int i = t; i; i--) printf("%d ", ans[i]); 83 }
1 #include <set> 2 #include <map> 3 #include <queue> 4 #include <stack> 5 #include <cmath> 6 #include <bitset> 7 #include <cstdio> 8 #include <string> 9 #include <vector> 10 #include <cstdlib> 11 #include <cstring> 12 #include <iostream> 13 #include <algorithm> 14 using namespace std; 15 16 typedef long long ll; 17 typedef pair<ll, ll> pll; 18 typedef pair<ll, int> pli; 19 typedef pair<int, ll> pil;; 20 typedef pair<int, int> pii; 21 typedef unsigned long long ull; 22 23 #define lson i<<1 24 #define rson i<<1|1 25 #define bug printf("********* "); 26 #define FIN freopen("D://code//in.txt", "r", stdin); 27 #define debug(x) cout<<"["<<x<<"]" <<endl; 28 #define IO ios::sync_with_stdio(false),cin.tie(0); 29 30 const double eps = 1e-8; 31 const int mod = 10007; 32 const int maxn = 1e4 + 7; 33 const double pi = acos(-1); 34 const int inf = 0x3f3f3f3f; 35 const ll INF = 0x3f3f3f3f3f3f3f; 36 37 int n, m, u, v, tot, top, t; 38 int head[maxn], vis[maxn*10]; 39 40 struct edge { 41 int v, next; 42 }ed[maxn*10]; 43 44 void addedge(int u, int v) { 45 ed[tot].v = v; 46 ed[tot].next = head[u]; 47 head[u] = tot++; 48 ed[tot].v = u; 49 ed[tot].next = head[v]; 50 head[v] = tot++; 51 } 52 53 void eulergraph(int x) { 54 for(int i = head[x]; ~i; i = ed[i].next) { 55 if(!vis[i]) { 56 vis[i] = 1; 57 eulergraph(ed[i].v); 58 } 59 } 60 printf("%d ", x); 61 } 62 63 int main() { 64 //FIN; 65 scanf("%d%d", &n, &m); 66 tot = top = t = 0; 67 memset(vis, 0, sizeof(vis)); 68 memset(head, -1, sizeof(head)); 69 for(int i = 1; i <= m; i++) { 70 scanf("%d%d", &u, &v); 71 addedge(u, v); 72 } 73 eulergraph(1); 74 return 0; 75 }