(hruscal12.3.3)POJ 3522 Slim Span(求解一个生成树使得该树中的最大边权值和最小边权值之差最小)

/* * POJ_2421.cpp * *  Created on: 2013年11月8日 *      Author: Administrator */#include <iostream>#include <cstdio>#include <cstring>#include <algorithm>#include <cmath>using namespace std;struct edge{int begin;int end;int weight;};const int maxn = 110;int father[maxn];edge e[maxn*maxn];int map[maxn][maxn];int n,m;int find(int x){if( x == father[x]){return x;}father[x] = find(father[x]);return father[x];}int kruscal(int start){//使用kruscal算法来生成最小生成树并计算带权路径和int i;int sum = 0;//用sum来记录最小s生成树的边权和    int max = INT_MIN;    int min = INT_MAX;    int count = 0;for( i = 1 ; i < maxn ; ++i){father[i] = i;}for( i = start ; i <= m ; ++i){//枚举有序边集中的每一条边int fx = find(e[i].begin);int fy = find(e[i].end);if(fx != fy){//若第k条边的两个端点i,j 分别属于两颗不同的子树father[fx] = fy;//则将节点i所在的子树并入节点j所在的子树中sum += e[i].weight;//求解每种生成树的(max - min)值count++;if(e[i].weight > max){max = e[i].weight;}if(e[i].weight < min){min = e[i].weight;}}}if(count != n-1){//不是生成树return -1;}return max - min;}bool compare(const edge& a , const edge& b){return a.weight < b.weight;}//以上是用kruscal算法来解决问题的基本模板.....int main(){while(scanf("%d%d",&n,&m)!=EOF,n||m){int i,j;for(i = 1 ; i <= m ; ++i){scanf("%d%d%d",&e[i].begin,&e[i].end,&e[i].weight);}sort(e+1,e+m+1,compare);//kruscal算法要求边有序..特别需要注意的是排序的起点和终点/** * * 求生成树中最大边权值和最小边权值之差最小的: * 枚举每一条边,将其作为下界,向右寻找一个上界... * 使得生成树的最大边权值-最小边权值的差最小 * */int slim = INT_MAX;slim = min(slim,kruscal(1));if(slim != -1){for(i = 2 ; i <= m ; ++i){int temp = kruscal(i);if(temp >= 0){slim = min(slim,temp);}}}printf("%d\n",slim);}return 0;}