2017 Training for Graph Theory

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 static const int MAXN = 1e3 + 10;
 4 static const int OO = 0x3fffffff;
 5 struct Node
 6 {
 7     int u , v , w;
 8 };
 9 
10 int father[MAXN];
11 int high[MAXN];
12 vector<Node> data;
13 int n , m;
14 int ans = OO;
15 
16 void Init()
17 {
18     for(int i = 0 ; i <= n ; ++i)
19     {
20         father[i] = i;
21         high[i] = 0;
22     }
23 }
24 
25 int FindSet(int x)
26 {
27     if(x != father[x])
28         father[x] = FindSet(father[x]);
29     return father[x];
30 }
31 
32 bool Same(int x , int y)
33 {
34     return (FindSet(x) == FindSet(y));
35 }
36 
37 void Unite(int x , int y)
38 {
39     x = FindSet(x) , y = FindSet(y);
40     if(x != y)
41     {
42         if(high[x] > high[y])
43             father[y] = x;
44         else
45         {
46             father[x] = y;
47             if(high[x] == high[y])
48                 ++high[y];
49         }
50     }
51 }
52 
53 int main()
54 {
55     scanf("%d%d" , &n , &m);
56     for(int i = 1 ; i <= m ; ++i)
57     {
58         int a , b , c;
59         scanf("%d%d%d" , &a , &b , &c);
60         data.push_back({a , b , c});
61     }
62 
63     sort(data.begin() , data.end() , [](Node a , Node b){return a.w < b.w;});
64     int mx , mi;
65     for(int i = 0 ; i < m ; ++i)
66     {
67         Init();
68         mi = data[i].w;
69         mx = mi;
70         Unite(data[i].u , data[i].v);
71         for(int j = i + 1 ; j < m ; ++j)
72         {
73             if(Same(1 , n))
74                 break;
75             if(!Same(data[j].u , data[j].v))
76             {
77                 Unite(data[j].u , data[j].v);
78                 mx = data[j].w;
79             }
80         }
81         if(Same(1 , n))
82             ans = min(ans , mx - mi);
83     }
84 
85     printf("%d" , ans);
86 }