1291. Gear-wheels

http://acm.timus.ru/problem.aspx?space=1&num=1291

dfs 遍历树的节点 根据齿轮数量的比 求得转速 注意用 gcd 化减

代码：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<set>
#include<queue>
#include<stack>
#include<map>
#include<string>
#include<iomanip>
using namespace std;

#define LL long long
const int INF=0x3f3f3f3f;
const int N=1005;
int head[N],I;
struct node
{
    int j,next;
}side[N*2];
bool visited[N];
int a[N];
int numerator[N];
int denominator[N];
void add(int i,int j)
{
    side[I].j=j;
    side[I].next=head[i];
    head[i]=I++;
}
int gcd(int x,int y)
{
    if(x%y==0)
    return y;
    return gcd(y,x%y);
}
void Fans(int x,int y)
{
    numerator[y]=-numerator[x]*a[x];
    denominator[y]=denominator[x]*a[y];
    int k=gcd(abs(numerator[y]),abs(denominator[y]));
    numerator[y]/=k;
    denominator[y]/=k;
}
void dfs(int x)
{
    visited[x]=true;
    for(int t=head[x];t!=-1;t=side[t].next)
    {
        int l=side[t].j;
        if(visited[l])
        continue;
        Fans(x,l);
        dfs(l);
    }
}
int main()
{
    //freopen("data.in","r",stdin);
    int n;
    while(cin>>n)
    {
        memset(head,-1,sizeof(head));
        I=0;
        for(int i=1;i<=n;++i)
        {
            cin>>a[i];
            int k;
            while(cin>>k)
            {
                if(!k)
                break;
                add(i,k);
            }
        }
        for(int i=1;i<=n;++i)
        {
            numerator[i]=0;
            denominator[i]=1;
        }
        int s,v;
        cin>>s>>v;
        numerator[s]=v;
        memset(visited,false,sizeof(visited));
        dfs(s);
        for(int i=1;i<=n;++i)
        cout<<numerator[i]<<"/"<<denominator[i]<<endl;
    }
    return 0;
}