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【LOJ119】单源最短路 模板


problem

  • 给你一个n个点m条边的无向图,求 s 到 t 的最短路。

solution

  • SPFA模板

codes

#include<iostream>
#include<queue>
#include<cstring>
#define maxn 2500+10
#define maxm 6200+10
using namespace std;
const int inf = 2147483647;

//Grape
int n, m, s, t;
struct Edge{int v, w, next;}e[maxm<<2];
int tot, head[maxn];
void AddEdge(int u, int v, int w){
tot++; e[tot].v=v; e[tot].w=w; e[tot].next=head[u]; head[u]=tot;
}

//SPFA
int dist[maxn], book[maxn];
queue<int>q;
void spfa(){
for(int i = 1; i <= n; i++)dist[i]=inf;
dist[s]=0; book[s]=1; q.push(s);
while(q.size()){
int u = q.front(); q.pop(); book[u]=0;
for(int i = head[u]; i != -1; i = e[i].next){
int v = e[i].v, w = e[i].w;
if(dist[v]>dist[u]+w){
dist[v] = dist[u]+w;
if(!book[v]){
book[v] = 1; q.push(v);
}
}
}
}
}

int main(){
memset(head,-1,sizeof(head));
cin>>n>>m>>s>>t;
for(int i = 1; i <= m; i++){
int x, y, z; cin>>x>>y>>z;
AddEdge(x,y,z); AddEdge(y,x,z);
}
spfa();
cout<<dist[t];
return 0;
}


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