HDU 5429 Geometric Progression

题意：给出一个大数数列，问是不是等比数列。

 

解法：拿java大数搞，注意全是0的情况也是Yes。我把公比用分数表示了，灰常麻烦，题解说只要判a[i - 1] * a[i + 1] == a[i] * a[i]就可以了，涨姿势了。

 

代码：

import java.math.*;
import java.util.Scanner;

public class Main
{
    public static void main(String[] args)
    {
        Scanner cin = new Scanner(System.in);
        while(cin.hasNext())
        {
            int T = cin.nextInt();
            while(T-- != 0)
            {
                boolean flag = false;
                BigInteger fenzi = BigInteger.ZERO;
                BigInteger fenmu = BigInteger.ZERO;
                boolean ans = true;
                BigInteger a0 = BigInteger.ZERO, a1 = BigInteger.ZERO;
                int n = cin.nextInt();
                for(int i = 0; i < n; i++)
                {
                    BigInteger x = cin.nextBigInteger();
                    if(!ans) continue;
                    if(i == 0)
                    {
                        if(x.equals(BigInteger.ZERO))
                        {
                            flag = true;
                        }
                        a0 = x;
                    }
                    else
                    {
                        if(flag)
                        {
                            if(!x.equals(BigInteger.ZERO))
                                ans = false;
                        }
                        else
                        {
                            if(x.equals(BigInteger.ZERO))
                            {
                                ans = false;
                                continue;
                            }
                            a1 = x;
                            if(i == 1)
                            {
                                BigInteger r = a0.gcd(a1);
                                fenzi = a1.divide(r);
                                fenmu = a0.divide(r);
                            }
                            else
                            {
                                BigInteger r = a0.gcd(a1);
                                if(!fenzi.equals(a1.divide(r)))
                                    ans = false;
                                if(!fenmu.equals(a0.divide(r)))
                                    ans = false;
                            }
                            a0 = a1;
                        }
                    }
                }
                if(ans)
                    System.out.println("Yes");
                else
                    System.out.println("No");
            }
        }
    }
}