Uva1395 & poj3522 -- slim span [Kruskal] bottleneck generation tree

Link:Http://uva.onlinejudge.org/index.php? Option = com_onlinejudge & Itemid = 8 & page = show_problem & problem = 4141

Question:N vertices and m edges are given, and a spanning tree is obtained to minimize the difference between the maximum edge and the minimum edge.

Ideas:Finding a spanning tree to minimize the maximum edge is the bottleneck spanning tree. For this question, we enumerate the minimum edge of each edge, find the maximum edge of the corresponding Minimum Spanning Tree, and find the minimum difference between the maximum edge and the minimum edge.

#include<cstring>#include<string>#include<fstream>#include<iostream>#include<iomanip>#include<cstdio>#include<cctype>#include<algorithm>#include<queue>#include<map>#include<set>#include<vector>#include<stack>#include<ctime>#include<cstdlib>#include<functional>#include<cmath>using namespace std;#define PI acos(-1.0)#define MAXN 50100#define eps 1e-7#define INF 0x7FFFFFFF#define LLINF 0x7FFFFFFFFFFFFFFF#define seed 131#define MOD 1000000007#define ll long long#define ull unsigned ll#define lson l,m,rt<<1#define rson m+1,r,rt<<1|1struct node{    int u,v,w;}edge[MAXN];int n,m,father[110],maxm;bool cmp(node x,node y){    return x.w<y.w;}int Find(int x){    int t = x;    while(t!=father[t])        t = father[t];    int k = x;    while(k!=t){        int temp = father[k];        father[k] = t;        k = temp;    }    return t;}bool kruskal(int x){    int i,j;    maxm = 0;    for(i=0;i<=n;i++)    father[i] = i;    int sum = 0;    for(i=x;i<m;i++){        int a = Find(edge[i].u);        int b = Find(edge[i].v);        if(a!=b){            father[a] = b;            sum++;            maxm = max(maxm,edge[i].w);            if(sum>=n-1)    return true;        }    }    return false;}int main(){    int i,j;    while(scanf("%d%d",&n,&m),n||m){        for(i=0;i<m;i++){            scanf("%d%d%d",&edge[i].u,&edge[i].v,&edge[i].w);        }        sort(edge,edge+m,cmp);        int ans = INF;        for(i=0;i<m;i++){            if(m-i<n-1) break;            if(kruskal(i)){                ans = min(ans,maxm-edge[i].w);            }        }        if(ans==INF)    puts("-1");        else        printf("%d\n",ans);    }    return 0;}

Uva1395 & poj3522 -- slim span [Kruskal] bottleneck generation tree