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

 1 #include <iostream>

 2 #include <cstdio>

 3 #include <cmath>

 4 #include <cstring>

 5 using namespace std;

 6

 7 int main()

 8 {

 9     int t, n, a, b, x;

10     scanf("%d", &t);

11     while(t--)

12     {

13         scanf("%d", &n);

14         x = -1;

15         for(b = sqrt(n); b >= 1; b--)

16         {

17             if(n%b==0)

18             {

19                 a = n/b;

20                 if(a>b && (a-b)%2==0)

21                 {

22                     x = (a-b)/2;

23                     break;

24                 }

25             }

26         }

27         printf("%d\n", x);

28     }

29     return 0;

30 }

hdu 4143 A Simple Problem (变形),布布扣,bubuko.com