hdu 4143 A Simple Problem (变形)

题目

题意：给n,求x;

直接枚举肯定超时， 把给的式子变形， （y+x）(y-x) = n;

令y-x = b, y+x = a;

枚举b, b 的范围肯定是sqrt(n),  y = (a+b)/2;  x = (a-b)/2;

b越大， x越小， 所以倒着枚举b

#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
using namespace std;

int main()
{
    int t, n, a, b, x;
    scanf("%d", &t);
    while(t--)
    {
        scanf("%d", &n);
        x = -1;
        for(b = sqrt(n); b >= 1; b--)
        {
            if(n%b==0)
            {
                a = n/b;
                if(a>b && (a-b)%2==0)
                {
                    x = (a-b)/2;
                    break;
                }
            }
        }
        printf("%d\n", x);
    }
    return 0;
}