多源点最短路径

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给出s个起点，给出t个终点，求出所有起点到终点的最短路中的最短的一个.

构建一个超级源点，与每一个起点相连，权值为0；构建一个超级终点，与每一个终点相连，权值为0。然后求超级源点到超级终点的最短路径。

#include<iostream>#include<queue>using namespace std;int first[1010], dist[1010];int point[202010], weight[202010], next[202010];int q[50000];bool f[1010];int n,m,s,t,tot;void addEdge(int x, int y, int w)  //边集数组保存图{    tot++;    point[tot] = y;    next[tot] = first[x];    first[x] = tot;    weight[tot] = w;    tot++;    point[tot] = x;    next[tot] = first[y];    first[y] = tot;    weight[tot] = w;}void spfa_slf(){    int h = 0;    int t = 0;    q[t] = 0; f[0] = true;    while (h <= t)    {        int now = q[h];        h++;        f[now] = false;        int k = first[now];        while (k != 0)        {            int New = point[k];            if (dist[now] + weight[k] < dist[New])            {                dist[New] = dist[now] + weight[k];                if (!f[New])                {                    t++;                    q[t] = New;                    f[New] = true;                }            }            k = next[k];        }    }}int main(){    while (cin>>n>>m>>s>>t && n && m && s && t)    {        tot = 0;        for (int i=1; i<=m; i++)        {            int x, y, w;            cin>>x>>y>>w;            addEdge(x,y,w);        }        for (int i=1; i<=s; i++)  //构建超级源点        {            int x;            cin>>x;            addEdge(0,x,0);        }        for (int i=1; i<=t; i++)  //构建超级终点        {            int x;            cin>>x;            addEdge(x,n+1,0);        }        for (int i=0; i<=n+1; i++)        {            dist[i] = (1<<30);            f[i] = false;        }        dist[0] = 0;        spfa_slf();  //spfa求最短路径        if (dist[n+1] < (1<<30))            cout<<dist[n+1]<<endl;        else            cout<<"What a pity!"<<endl;        for (int i=0; i<=n+1; i++)            first[i] = dist[i] = f[i] = 0;        for (int i=0; i<=tot; i++)            point[i] = next[i] = weight[i] = 0;    }    return 0;}

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