hiho刷题日记——第二十五天最短路径·三：SPFA算法

题目

思路

代码

#include<cstdio>
#include<cstring>
using namespace std;

const int MAXN=100000+1;
const int MAXM=1000000+1;
int N,M,S,T,head[MAXN],queue[MAXM],front=0,rear=0,e=0;
int ans[MAXN];
struct EDGE
{
int v,next,cost;
}edge[MAXM<<1];

void addEdge(int x,int y,int z)
{
edge[e].v=y;
edge[e].cost=z;
edge[e].next=head[x];
head[x]=e++;
}

void bfs(int x)
{
queue[rear++]=x;
while(front<rear)
{
x=queue[front++];
for(int p=head[x];p!=-1;p=edge[p].next)
if(ans[edge[p].v]==-1 || ans[x]+edge[p].cost<ans[edge[p].v])
{
ans[edge[p].v]=ans[x]+edge[p].cost;
queue[rear++]=edge[p].v;
}
}
}

int main()
{
memset(head,-1,sizeof(head));
memset(ans,-1,sizeof(ans));
scanf("%d%d%d%d",&N,&M,&S,&T);

int a,b,c;
while(M--)
{
scanf("%d%d%d",&a,&b,&c);
addEdge(a,b,c);
addEdge(b,a,c);
}

ans[S]=0;
bfs(S);

printf("%d",ans[T]);

return 0;
}