poj 1041 John's trip (Euler Circuit)

　　输出字典序最小的欧拉回路。之前做过的是要求点的序列最小字典序，今天见到这个经典的欧拉回路是要输出边的编号的最小序。做法跟输出点路径的相似。

View Code

 1 #include <cstdio>
 2 #include <iostream>
 3 #include <algorithm>
 4 #include <set>
 5 #include <map>
 6 #include <queue>
 7 #include <stack>
 8 
 9 using namespace std;
10 
11 typedef pair<int, int> PII;
12 typedef multiset<PII> MTPII;
13 #define ITOR iterator
14 #define MPR make_pair
15 #define FI first
16 #define SE second
17 #define REP(i, n) for (int i = 0; i < (n); i++)
18 const int N = 50;
19 MTPII rel[N];
20 map<int, int> nextVex[N];
21 int roadCnt;
22 
23 int input() {
24     roadCnt = 0;
25     int x, y, z, mk = 0;
26     REP(i, N) rel[i].clear(), nextVex[i].clear();;
27     while (cin >> x >> y && (x || y)) {
28         cin >> z;
29         if (!roadCnt) {
30             mk = min(x, y);
31         }
32         rel[x].insert(MPR(z, y));
33         nextVex[x][z] = y;
34         rel[y].insert(MPR(z, x));
35         nextVex[y][z] = x;
36         roadCnt++;
37     }
38     return mk;
39 }
40 
41 stack<int> path;
42 
43 int check(int mk) {
44     REP(i, N) if (rel[i].size() & 1) return -1;
45     stack<int> tmp = path;
46     int sz = tmp.size(), t;
47     REP(i, sz) {
48         t = tmp.top();
49         tmp.pop();
50         if (nextVex[mk].find(t) == nextVex[mk].end()) return -1;
51         mk = nextVex[mk][t];
52     }
53     return mk;
54 }
55 
56 void dfs(int x) {
57     while (!rel[x].empty()) {
58         int edge = (*rel[x].begin()).FI, nx = (*rel[x].begin()).SE;
59         rel[x].erase(rel[x].begin());
60         rel[nx].erase(MPR(edge, x));
61         dfs(nx);
62         path.push(edge);
63     }
64 }
65 
66 void output() {
67     int sz = path.size();
68     REP(i, sz) {
69         if (i) putchar(' ');
70         printf("%d", path.top());
71         path.pop();
72     }
73     puts("");
74 }
75 
76 int main() {
77 //    freopen("in", "r", stdin);
78     int mk;
79     while (mk = input()) {
80         while (!path.empty()) path.pop();
81         dfs(mk);
82         if ((path.size() == roadCnt) && (check(mk) == mk)) output();
83         else puts("Round trip does not exist.");
84     }
85     return 0;
86 }

——written by Lyon

posted @ 2013-05-01 02:26 LyonLys 阅读(204) 评论(0) 收藏举报

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