SOJ4339 Driving Range 最小生成树 kruskal算法

 1 #include <iostream>
 2 #include <cstdio>
 3 #include <cstring>
 4 #include <cmath>
 5 #include <string>
 6 #include <iterator>
 7 #include <algorithm>
 8 #include <cstdlib>
 9 #include <deque>
10 #include <queue>
11 #include <stack>
12 #include <map>
13 #include <vector>
14 #include <set>
15 #include <list>
16 using namespace std;
17 #define PI acos(-1.0)
18 #define INF 0x3f3f3f3f
19 #define MAX 1000005
20 #define MST(a,b) memset(a,b,sizeof(a))
21 #define MOD 1000000007
22 #define EPS 1e-6
23 typedef long long LL;
24 typedef unsigned long long LLU;
25 int n,m;
26 int r[MAX],u[MAX],v[MAX],w[MAX],p[MAX];
27 int cmp(const int i,const int j) {
28     return w[i] < w[j];
29 }
30 int find(int x) {
31     return p[x] == x ? x : p[x] = find(p[x]);
32 }
33 int kruskal() {
34     int ans = 0;
35     for(int i = 0;i < n;i ++)
36         p[i] = i;
37     for(int i = 0;i < m;i ++)
38         r[i] = i;
39     sort(r,r + m,cmp);
40     int flag = 1;
41     for(int i = 0;i < m;i ++) {
42         int e = r[i];
43         int x = find(u[e]);
44         int y = find(v[e]);
45         if(x != y) {
46             ans = max(ans,w[e]);
47             p[x] = y;
48             flag ++;
49         }
50     }
51     if(flag != n)
52         return 0;
53     return ans;
54 }
55 int main() {
56     while(scanf("%d%d",&n,&m) && (n || m)) {
57         for(int i = 0;i < m;i ++) {
58             int s,t,l;
59             scanf("%d%d%d",&s,&t,&l);
60             w[i]= l;
61             u[i] = s;
62             v[i] = t;
63         }
64         int ans = kruskal();
65         if(ans)
66             printf("%d\n",ans);
67         else
68             printf("IMPOSSIBLE\n");
69     }
70     return 0;
71 }