qiaoxu123
12/8/2018 - 11:10 AM

50. Pow(x, n)

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 [−231, 231 − 1]
test1.cpp
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class Solution {
public:
    double myPow(double x, int n) {
    	double ans = 1;
    	unsigned long long p;
    	if (n < 0) {
    		p = -n;
    		x = 1 / x;
    	} 
        else
    		p = n;
        
		while (p) {
			if (p & 1)
				ans *= x;
			x *= x;
			p >>= 1;
		}
		return ans;
    }
};