poj slim span

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#include <bits/stdc++.h>using namespace std;#define N 105#define INF 0x7ffffffstruct Edge{    int u;    int v;    int w;}edge[N*N/2];int n, m, span, p[N], rank[N];int cmp(Edge a, Edge b){    return a.w<b.w;}int find(int x){    return p[x] == x ? x : p[x] = find(p[x]);}void unionSet(int x, int y){    if (rank[x] > rank[y]) p[y] = x;    else {        p[x] = y;        if (rank[x] == rank[y]) rank[y]++;    }}void kruskal(){    sort(edge+1, edge+m+1, cmp);    for(int i=1; i<=m-n+2; i++)      {          int cnt = 0;          int start = 0;          for(int j=1; j<=n; j++) p[j] = j;          memset(rank, 0, sizeof(rank));          for(int k=i; k<=m; k++)          {              int x = find(edge[k].u);              int y = find(edge[k].v);              if(x != y)              {                  unionSet(x,y);                  cnt++;                  if(!start)                   start = i;                  if(cnt == n-1)                  {                      span = min(span, edge[k].w-edge[start].w);                      break;                  }              }          }      }      if(span == INF) cout<<-1<<endl;      else cout<<span<<endl;}int main(){      while(~scanf("%d%d",&n, &m) && n+m)    {        for(int i=1; i<=m; i++)        cin>>edge[i].u>>edge[i].v>>edge[i].w;        span = INF;        kruskal();    }    return 0;}
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