[leetcode]-50. Pow(x, n)(C语言)

Implement pow(x, n), which calculates x raised to the power n (xn).

Example 1:

Input: 2.00000, 10
Output: 1024.00000

Example 2:

Input: 2.10000, 3
Output: 9.26100

Example 3:

Input: 2.00000, -2
Output: 0.25000
Explanation: 2-2 = 1/22 = 1/4 = 0.25

Note:

  • -100.0 < x < 100.0
  • n is a 32-bit signed integer, within the range [−2^31, 2^31 − 1]
double ppow(double x,int n)
{
    if(n==0)
        return 1;
    if(n==1)
        return x;
    if(x==0)
        return 0;
    double res;
    res=ppow(x,n/2);
    if(n%2==1)
        return res*res*x;
    else
        return res*res;
}
double myPow(double x, int n) {
    if(x==0)
        return 0;
    if(n==0)
        return 1;
    double res=1.0,ans;
    if(n>0)
    {
        res=ppow(x,n);
        return res;
    }
    else
    {
        ans=x*ppow(x,-(n+1));
        res=1.0/ans;
    }
    return res;
}

 

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