洛谷P1525 关押罪犯 并查集

 1 #include <cstdio>
 2 #include <cmath>
 3 #include <cstdlib>
 4 #include <cstring>
 5 #include <string>
 6 #include <algorithm>
 7 #include <iomanip>
 8 #include <iostream> 
 9 #define ll int 
10 using namespace std ; 
11 
12 const int maxn = 20011,maxm = 100011 ; 
13 ll n,m,u,v ; 
14 ll fa[2*maxn] ; 
15 struct node{
16     ll from,to,val ; 
17 }e[maxm] ; 
18 
19 inline ll read() 
20 {
21     char ch = getchar() ; 
22     ll x = 0 ,f = 1 ; 
23     while(ch<‘0‘||ch>‘9‘) { if(ch==‘-‘) f = -1 ; ch = getchar() ; }    
24     while(ch>=‘0‘&&ch<=‘9‘) { x = x*10+ch - 48 ; ch = getchar() ; } 
25     return x*f ; 
26 }
27 
28 inline bool cmp(node a,node b) 
29 {
30     return a.val > b.val ; 
31 }
32 
33 inline ll getfather(int x) 
34 {
35     if(fa[x]==x) return x ; 
36     fa[ x ] = getfather(fa[ x ]) ; 
37     return fa[ x ] ;  
38 }
39 
40 int main()
41 {
42     n = read() ;  m = read() ; 
43     for(int i=1;i<=m;i++) 
44         e[ i ].from = read(),e[ i ].to = read(),e[ i ].val = read() ; 
45         
46     sort(e+1,e+m+1,cmp) ;
47     for(int i=1;i<=2*n;i++) fa[ i ] = i ; 
48     for(int i=1;i<=m;i++) 
49     {
50         u = getfather(e[ i ].from) ; 
51         v = getfather(e[ i ].to) ; 
52         if( u==v ) 
53         {
54             printf("%d\n",e[ i ].val) ; 
55             return 0 ; 
56         } 
57         fa[ u ] = getfather( e[ i ].to+n ) ; // 注意这边是 fa[ getfather( e[ i ].from ) 
58         fa[ v ] = getfather( e[ i ].from+n ) ; 
59     } 
60     printf("0\n") ; 
61     return 0 ; 
62 }