最短路

Posted 2021-01-04 civilization-ga

spfa会被卡 试试dijskstra

没想到这个题写了 2h 结果是读入优化写错了

rio

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
#include<cstring>
#define maxn 500010 
#define maxx 500010
#define inf 2147483647
using namespace std;

//typedef pair<long long,int> pa;

//priority_queue<pa,vector<pa>,greater<pa> >q;

priority_queue< pair<int,int> > q;

int n,head[maxx];

long long dis[maxx];

int vis[maxx];

int m,s,cnt;

void read(int &x){
    x=0;int flag=1;char c=getchar();
    while(c<‘0‘||c>‘9‘) flag=(c==‘-‘?-1:1),c=getchar();
    while(c>=‘0‘&&c<=‘9‘) x=x*10+c-‘0‘,c=getchar();
    x=x*flag;
}

struct Edge{
    int u,v;
    long long w;
}edge[maxn];

void add(int u,int v,long long w){//nex
    edge[++cnt].v=v;//to
    edge[cnt].w=w;//v
    edge[cnt].u=head[u];
    head[u]=cnt;//fr
}

void dijs(){
    memset(vis,0,sizeof(vis));
    for(int i=1;i<=n;i++) dis[i]=inf;
    dis[s]=0;
    q.push(make_pair(0,s));
    while(!q.empty()){
      int now=q.top().second;q.pop();
      if(vis[now]) continue;
      vis[now]=1;
      for(int i=head[now];i;i=edge[i].u){
          int v=edge[i].v;
          if(dis[v]>dis[now]+edge[i].w) {
              dis[v]=dis[now]+edge[i].w;
              q.push(make_pair(-dis[v],v));
          }
       }        
    }
} 

int main(){
    read(n);read(m);read(s);
    for(int i=1;i<=m;i++){
        int u,v,w;
        read(u);read(v);read(w);
        add(u,v,w);
    }
    dijs(); 
    for(int i=1;i<=n;i++) cout<<dis[i]<<" ";
}