csu1307_City Tour

#include <iostream>#include <cstdio>#include <memory.h>#include <queue>using namespace std;int v[100008],next[100008],w[100008];int first[1002],d[1002],e;typedef pair<int,int> pii;void init(){    e = 0;    memset(first,-1,sizeof(first));}void add_edge(int a,int b,int c){    v[e] = b;next[e] = first[a];    w[e] = c;first[a] = e ++;}int dijkstra(int src,int dist,int maxlen){    memset(d,-1,sizeof(d));    priority_queue<pii,vector<pii>,greater<pii> > q;    d[src] = 0;    q.push(make_pair(0,src));    while(!q.empty()){        while(!q.empty() && q.top().first > d[q.top().second]) q.pop();        if(q.empty()) break;        int u = q.top().second; q.pop();        for(int i = first[u];i != -1;i = next[i]) if(w[i] <= maxlen){            if(d[v[i]] == -1 || d[v[i]] > d[u] + w[i]){                d[v[i]] = d[u] + w[i];                q.push(make_pair(d[v[i]],v[i]));            }        }    }    return d[dist];}int main(){    int n,m,a,b;    while(~scanf("%d %d %d %d",&n,&m,&a,&b)){        init();        int x1,x2,x3,l = 0x3f3f3f3f,r = -1;        for(int i = 0;i < m;i ++){            scanf("%d %d %d",&x1,&x2,&x3);            add_edge(x1,x2,x3);            add_edge(x2,x1,x3);            l = min(l,x3);            r = max(r,x3);        }        int ans = -1;        while(l <= r){            int mid = (l + r) / 2;            if(dijkstra(a,b,mid) == -1){                l = mid + 1;            }            else{                r = mid - 1;                ans = dijkstra(a,b,mid);            }        }        printf("%d\n",ans);    }    return 0;}

dijkstra问题。