http://acm.hdu.edu.cn/showproblem.php?pid=1598
题意：中文题
题解：枚举+最小生成树(Kruskal)。对于每个要查询的s，e，枚举边。总是忘记minn初始化……
1 #include <iostream> 2 #include <cstring> 3 #include <cstdio> 4 #include <cstdlib> 5 #include <cmath> 6 #include <string> 7 #include <vector> 8 #include <list> 9 #include <map> 10 #include <queue> 11 #include <stack> 12 #include <bitset> 13 #include <algorithm> 14 #include <numeric> 15 #include <functional> 16 #include <set> 17 #include <fstream> 18 19 using namespace std; 20 21 const int INF=0xfffffff; 22 const int maxn=2010; 23 24 int N,M; 25 int V,E; 26 27 int par[maxn]; 28 int rankh[maxn]; 29 struct edge{ 30 int u,v,cost; 31 }; 32 edge es[maxn]; 33 34 bool cmp(const edge& e1,const edge& e2) 35 { 36 return e1.cost<e2.cost; 37 } 38 39 void init(int n) 40 { 41 for(int i=0;i<=n;i++) 42 { 43 par[i]=i; 44 rankh[i]=0; 45 } 46 } 47 48 int find(int x) 49 { 50 if(par[x]==x) 51 { 52 return x; 53 } 54 else{ 55 return par[x]=find(par[x]); 56 } 57 } 58 59 /*int find(int x) 60 { 61 while(x!=par[x]) x=par[x]; 62 return x; 63 }*/ 64 65 void unite(int x,int y) 66 { 67 x=find(x); 68 y=find(y); 69 if(x==y) return; 70 if(rankh[x]<rankh[y]){ 71 par[x]=y; 72 } 73 else{ 74 par[y]=x; 75 if(rankh[x]==rankh[y]) rankh[x]++; 76 } 77 } 78 79 bool same(int x,int y) 80 { 81 return find(x)==find(y); 82 } 83 84 int main() 85 { 86 //freopen("/Users/apple/Desktop/暑假/10/10/in","r",stdin); 87 while(scanf("%d%d",&N,&M)!=EOF) 88 { 89 V=N; 90 E=M; 91 int minn; 92 for(int i=0;i<M;i++) 93 { 94 scanf("%d%d%d",&es[i].u,&es[i].v,&es[i].cost); 95 // printf("%d %d %d ",es[i].u,es[i].v,es[i].cost); 96 } 97 // puts("asdfghjkl"); 98 sort(es,es+E,cmp); 99 // for(int i=0;i<M;i++) 100 // { 101 // printf("%d %d %d ",es[i].u,es[i].v,es[i].cost); 102 // } 103 int Q; 104 scanf("%d",&Q); 105 while(Q--) 106 { 107 int s,e; 108 scanf("%d%d",&s,&e); 109 minn=INF; 110 for(int i=0;i<E;i++) 111 { 112 init(V); 113 for(int j=i;j<E;j++) 114 { 115 int a=find(es[j].u); 116 int b=find(es[j].v); 117 if(a!=b) unite(a,b); 118 if(find(s)==find(e)) 119 { 120 minn=min(minn,es[j].cost-es[i].cost); 121 //printf("%d ",minn); 122 break; 123 } 124 } 125 } 126 if(minn==INF) puts("-1"); 127 else printf("%d ",minn); 128 //puts(""); 129 } 130 131 } 132 133 return 0; 134 }