HDU1598 ——find the most comfortable road(並查集)

將邊按速度進行從小達到的排序，設i是最大速度的邊，通過枚舉比i小的邊 for(j=i;j>=0;j--)  如果找到起點和終點在同一個集合裡，更新min。

測試資料較小，枚舉不會逾時。

#include<iostream>#include<algorithm>#include<cstdio>using namespace std;#define maxn 400#define INF 100000001int father[maxn],rank[maxn],n;struct Len{int start;int end;int speed;}len[1015];bool cmp(Len a,Len b){return a.speed<b.speed;}void makeset(){int i;for(i=1;i<=n;i++){father[i]=i;rank[i]=0;}}int getfather(int v){    if (father[v]==v)      return v;    else    {        father[v]=getfather(father[v]);        return father[v];     }}void Union(int x,int y){int fx,fy;    fx=getfather(x);    fy=getfather(y);    if(fy!=fx)       father[fx]=fy;}bool same(int x,int y){   return getfather(x)==getfather(y);}void judge(int x ,int y) {int fx,fy;     fx = getfather(x);     fy = getfather(y);     if (rank[fx]>rank[fy])        father[fy] = fx;     else     {        father[fx] = fy;        if(rank[fx]==rank[fy])           ++rank[fy];     }}int main(){int m;int min;int i,j;while(scanf("%d%d",&n,&m)!=EOF){for(i=0;i<m;i++)scanf("%d%d%d",&len[i].start,&len[i].end,&len[i].speed);sort(len,len+m,cmp);int q,s,e;int k,f;scanf("%d",&q);for(k=0;k<q;k++){min=INF;scanf("%d%d",&s,&e);for(i=0;i<m;i++){makeset();for(j=i;j>=0;j--){Union(len[j].start,len[j].end);judge(len[j].start,len[j].end);if(same(s,e)){if(min>len[i].speed-len[j].speed)min=len[i].speed-len[j].speed;break;}}}if(min!=INF)printf("%d\n",min);elseprintf("-1\n");}}return 0;}