hdu1496(hash)

Equations

Equation

Time Limit: 6000/3000 MS (Java/Others)   

Memory Limit: 32768/32768 K (Java/Others)

Total Submission(s): 5535    Accepted Submission(s): 2196

题目链接： http://acm.hdu.edu.cn/showproblem.php?pid=1496

Problem Description

Consider equations having the following form:

a*x1^2+b*x2^2+c*x3^2+d*x4^2=0
a, b, c, d are integers from the interval [-50,50] and any of them cannot be 0.

It is consider a solution a system ( x1,x2,x3,x4 ) that verifies the equation, xi is an integer from [-100,100] and xi != 0, any i ∈{1,2,3,4}.

Determine how many solutions satisfy the given equation.

 

Input

The input consists of several test cases. Each test case consists of a single line containing the 4 coefficients a, b, c, d, separated by one or more blanks.
End of file.

 

Output

For each test case, output a single line containing the number of the solutions.

 

Sample Input

1 2 3 -4 1 1 1 1

 

Sample Output

39088 0 解题思路： 题意就是满足公式的x1,x2,x3,x4有多少种。 暴力O（n^4）超时·····hash优化···直接降到了O（n^2）····· 可以建立两个数组，首先计算a * x1 ^ 2 + b * x2 ^ 2，正数存入hash1,负数存入hash2。然后计算c * x3 ^ 2 + d * x4 ^ 2，如果是正数则在hash2查找， 负数在hash1查找。 完整代码：

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