URAL 1291 Gear-wheels（BFS）

#include <iostream>
#include <cstring>
#include <cstdio>
#include <algorithm>
#include <cmath>
#include <string>
#include <map>
#include <stack>
#include <queue>
#include <vector>
#define inf 0x3f3f3f3f
#define met(a,b) memset(a,b,sizeof a)
#define pb push_back
typedef long long ll;
using namespace std;
const int N = 1e3+10;
const int M = 124750+10;
const int mod=1e9+7;
int n,m,k,tot=0,s,t,v;
int head[N],vis[N],speed[N],sum[N];
struct ANS{int f,s;}ans[N];
struct EDG{int to,next;}edg[N*N];
void add(int u,int v){
    edg[tot].to=v;edg[tot].next=head[u];head[u]=tot++;
}
int gcd(int x,int y){
    int xx=x,yy=y;
    x=max(xx,yy);
    y=min(yy,xx);
    if(x%y==0)return y;
    return gcd(x-y,y);
}
void bfs(){
    queue<int>q;
    q.push(s);vis[s]=1;ans[s].f=t;ans[s].s=1;
    while(!q.empty()){
        int u=q.front();q.pop();//printf("!!!%d %d %d\n",u,ans[u].f,ans[u].s);system("pause");
        for(int i=head[u];i!=-1;i=edg[i].next){
            int v=edg[i].to;
            if(!vis[v]){
                vis[v]=1;
                int g=gcd(abs(sum[u]*ans[u].f),sum[v]*ans[u].s);
                ans[v].f=-sum[u]*ans[u].f/g;ans[v].s=sum[v]*ans[u].s/g;
                q.push(v);
            }
        }
    }
}
int main()
{
    met(ans,0);met(head,-1);
    int u,v;
    scanf("%d",&n);
    for(int u=1;u<=n;u++){
        scanf("%d",&sum[u]);
        while(~scanf("%d",&v)&&v){
            add(u,v);add(v,u);
        }
    }
    scanf("%d%d",&s,&t);
    bfs();
    for(int i=1;i<=n;i++){
        if(ans[i].f>0){
            printf("%d/%d\n",ans[i].f,ans[i].s);
        }else if(ans[i].f==0){
            printf("0/1\n");
        }else {
            printf("-%d/%d\n",-ans[i].f,ans[i].s);
        }
    }
    return 0;
}