poj 1679（次小生成树）

题意：让你判断最小生成树的值是不是唯一的。

思路：就是说若是存在次小生成树的值与最小生成树相同， 以前都喜欢用倍增法实现查出在最小生成树添加新边后环上最大权值的边，现在改用dfs复杂度少去一个logn。

代码如下：

 1 /**************************************************
 2  * Author     : xiaohao Z
 3  * Blog     : http://www.cnblogs.com/shu-xiaohao/
 4  * Last modified : 2014-02-10 15:50
 5  * Filename     : poj_1679.cpp
 6  * Description     : 
 7  * ************************************************/
 8 
 9 #include <iostream>
10 #include <cstdio>
11 #include <cstring>
12 #include <cstdlib>
13 #include <cmath>
14 #include <algorithm>
15 #include <queue>
16 #include <stack>
17 #include <vector>
18 #include <set>
19 #include <map>
20 #define MP(a, b) make_pair(a, b)
21 #define PB(a) push_back(a)
22 
23 using namespace std;
24 typedef long long ll;
25 typedef pair<int, int> pii;
26 typedef pair<unsigned int,unsigned int> puu;
27 typedef pair<int, double> pid;
28 typedef pair<ll, int> pli;
29 typedef pair<int, ll> pil;
30 
31 const int INF = 0x3f3f3f3f;
32 const double eps = 1E-6;
33 const int LEN = 101;
34 int Map[LEN][LEN];
35 int n, m, top, fa[LEN], dis[LEN][LEN], tag[LEN*LEN], vis[LEN];
36 struct E{
37     int u, v, val;
38 }edge[LEN*LEN];
39 
40 bool cmp(E a, E b){return a.val < b.val;}
41 void init(){for(int i=0; i<LEN; i++) fa[i] = i;}
42 int Find(int x){return fa[x] == x ? x : fa[x] = Find(fa[x]);}
43 
44 int kruskal(){
45     int cnt = 0, ret = 0;
46     init();
47     memset(tag, 0, sizeof tag);
48     sort(edge, edge+m, cmp);
49     for(int i=0; i<m; i++){
50         int pa = Find(edge[i].u), pb = Find(edge[i].v);
51         if(pa == pb) continue;
52         fa[pa] = pb;
53         cnt ++;
54         Map[edge[i].u][edge[i].v] = Map[edge[i].v][edge[i].u] = edge[i].val;
55         tag[i] = 1;
56         ret += edge[i].val;
57         if(cnt == n-1) break;
58     }
59     return ret;
60 }
61 
62 void dfs(int bg, int v, int val){
63     vis[v] = 1;
64     dis[bg][v] = val;
65     for(int i=1; i<=n; i++){
66         if(Map[v][i] != INF && vis[i] == 0) dfs(bg, i, max(val, Map[v][i]));
67     }
68 }
69 
70 int main()
71 {
72 //    freopen("in.txt", "r", stdin);
73 
74     int T;
75     scanf("%d", &T);
76     while(T--){
77         memset(Map, 0x3f, sizeof Map);
78         memset(dis, 0, sizeof dis);
79         scanf("%d%d", &n, &m);
80         for(int i=0; i<m; i++){
81             scanf("%d%d%d", &edge[i].u, &edge[i].v, &edge[i].val);
82         }
83         int ans = kruskal();
84         for(int i=1; i<=n; i++){
85             memset(vis, 0, sizeof vis);
86             dfs(i, i, 0);
87         }
88         int f = 1;
89         for(int i=0; i<m; i++){
90             if(tag[i])continue;
91             if(edge[i].val == dis[edge[i].u][edge[i].v]) f = 0;
92         }
93         if(f)printf("%d\n", ans);
94         else printf("Not Unique!\n");
95     }
96     return 0;
97 }
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posted @ 2014-02-10 16:54  张小豪  阅读(760)  评论(0)  编辑  收藏  举报