【SDUTOJ 3309】 乱七八糟的图 (最短路+枚举最短路上的边)

【SDUTOJ 3309】 乱七八糟的图

题意翻译过来就是找构成最短路需要的最短的边长 因为存在一些最短路会共用一些边 所以求一遍最短路 然后遍历所有点 判断与该点连的边是否是构成最短路所需的边 把满足条件的边中最短的加入即可 即为到达该点所需要的边

代码如下:

#include <bits/stdc++.h>#define ll long longusing namespace std;typedef struct Edge{    int v,w,next;}Edge;Edge eg[666666];int head[33333];ll dis[33333];bool vis[33333];int tp;void spfa(int u){    memset(dis,-1,sizeof(dis));    memset(vis,0,sizeof(vis));    dis[u] = 0;    deque <int> q;    int i,v,w;    q.push_front(u);    while(!q.empty())    {        u = q.front();        q.pop_front();        vis[u] = 0;        for(i = head[u]; i != -1; i = eg[i].next)        {            v = eg[i].v;            w = eg[i].w;            if(dis[v] == -1 || dis[v] > dis[u]+w) dis[v] = dis[u]+w;            else continue;            if(vis[v]) continue;            if(q.empty()) q.push_front(v);            else if(dis[v] < dis[q.front()]) q.push_front(v);            else q.push_back(v);            vis[v] = 1;        }    }}void Add(int u,int v,int w){    eg[tp].v = v;    eg[tp].w = w;    eg[tp].next = head[u];    head[u] = tp++;}int main(){    int n,m,st,u,v,w,i,j;    ll sum,mm;    while(~scanf("%d %d",&n,&m))    {        memset(head,-1,sizeof(head));        tp = 0;        while(m--)        {            scanf("%d %d %d",&u,&v,&w);            Add(u,v,w);            Add(v,u,w);        }        scanf("%d",&st);        spfa(st);        sum = 0;        for(i = 1; i <= n; ++i)        {            if(i == st) continue;            mm = 0;            for(j = head[i]; j != -1; j = eg[j].next)            {                if(dis[i] == dis[eg[j].v] + eg[j].w)                {                    if(!mm || mm > eg[j].w) mm = eg[j].w;                }            }            sum += mm;        }        printf("%lld\n",sum);    }    return 0;}