80分求调（wgzs

#include<bits/stdc++.h>
using namespace std;
const int N=1e5+5;
int n,m,a,b,v[N];
vector<int>g[2*N];
queue<int>q;
queue<int>dis;
int vis[N]; 
bool flag;
void bfs(){
    while(!q.empty()){
        int t=q.front();
        q.pop();
        int dist=dis.front();
        dis.pop();
        if(q.front()==b){
            cout<<dist+v[b]-v[a];
            flag=1;
            return;
        }
        for(int i=0;i<g[t].size();i++){
            if(vis[g[t][i]]==0){
                vis[g[t][i]]=1;
                q.push(g[t][i]);
                dis.push(dist+1);
            }
        }
    }
}
int main(){
    cin>>n>>m>>a>>b;
    a++,b++;
    for(int i=1;i<=n;i++)cin>>v[i];
    for(int i=1;i<=m;i++){
        int x,y;
        cin>>x>>y;
        x++,y++;
        g[x].push_back(y);
    }
    q.push(a);
    dis.push(0);
    vis[a]=1;
    flag=0;
    bfs();
    if(!flag)cout<<"No solution";
    return 0;
}