Spfa（最短路求解）

spfa（最短路求解）

模板：

#include<iostream>  
#include<cstdio>  
#include<queue>  
#include<cstring>  
using namespace std;  
const int maxn = 105;  
const int maxm = 100005;  
struct Edge{  
    int to,w,next;  
}edge[maxm<<1];  
int tot = 0,dis[maxn],cnt[maxn],head[maxn];  
  
void addedge(int u,int v,int w)  
{  
    edge[tot].to = v;edge[tot].w = w;edge[tot].next = head[u];  
    head[u] = tot++;  
}  
  
void spfa(int st,int ed)  
{  
    int i;  
    queue<int>que;  
    while (!que.empty())    que.pop();  
    memset(dis,0x3f3f3f3f,sizeof(dis));  
    memset(cnt,0,sizeof(cnt));  
    que.push(st);  
    dis[st] = 0;  
    cnt[st] = 1;  
    while (!que.empty())  
    {  
        int u = que.front();  
        que.pop();  
        if (u == ed)    continue;  
        for (i = head[u];i != -1;i = edge[i].next)  
        {  
            int v = edge[i].to;  
            if (dis[u] + edge[i].w < dis[v])  
            {  
                dis[v] = dis[u] + edge[i].w;  
                if (!cnt[v])    que.push(v);  
                cnt[v] = cnt[u];  
            }  
            else if (dis[u] + edge[i].w == dis[v])  
            {  
                if (!cnt[v])    que.push(v);  
                cnt[v] += cnt[u];  
            }  
        }  
    }  
}  
  
int main()  
{  
    int N,M,S,E,u,v,w,i;  
    memset(head,-1,sizeof(head));  
    scanf("%d%d%d%d",&N,&M,&S,&E);  
    while (M--)  
    {  
        scanf("%d%d%d",&u,&v,&w);  
        addedge(u,v,w);  
        addedge(v,u,w);  
    }  
    spfa(S,E);  
    printf("%d %d
",dis[E],cnt[E]);  
    return 0;  
}  

也可以计算有多少个最小生成树