codeforces 305B. Continued Fractions（数学）

A continued fraction of height n is a fraction of form . You are given two rational numbers, one is represented as and the other one is represented as a finite fraction of height n. Check if they are equal.
Input

The first line contains two space-separated integers p, q (1 ≤ q ≤ p ≤ 1018) — the numerator and the denominator of the first fraction.

The second line contains integer n (1 ≤ n ≤ 90) — the height of the second fraction. The third line contains n space-separated integers a1, a2, …, an (1 ≤ ai ≤ 1018) — the continued fraction.

Please, do not use the %lld specifier to read or write 64-bit integers in С++. It is preferred to use the cin, cout streams or the %I64d specifier.
Output

Print “YES” if these fractions are equal and “NO” otherwise.
Examples
Input

9 4
2
2 4

Output

YES

Input

9 4
3
2 3 1

Output

YES

Input

9 4
3
1 2 4

Output

NO

Note

In the first sample .

In the second sample .

In the third sample .

解题思路：

注意翻转分子和分母，每次减去假分数的部分就行了。

#include<iostream>using namespace std;__int64 s[100005];int main(){    __int64 a,b,n,i;    while(cin>>a>>b)    {        cin>>n;        for(i=0;i<n;i++)          cin>>s[i];        for(i=0;i<n;i++)        {            if(b==0||a/b<s[i])              break;            a-=s[i]*b;            swap(a,b);        }        if(i==n&&b==0)          cout<<"YES"<<endl;        else          cout<<"NO"<<endl;    }     return 0;}