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  • 50. Pow(x, n)

    Implement pow(xn), 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]

    binary search + 递归,注意n < 0时的处理

    time: O(logN), space: O(logN) -- need extra space to store the computation results, there are logN computations in total

    class Solution {
        public double myPow(double x, int n) {
            if (n < 0)
                return 1 / helper(x, -n);
            
            return helper(x, n);
        }
        private double helper(double x, int n) {
            if (n == 0) return 1;
            
            double half = helper(x, n / 2);
            if (n % 2 == 0)
                return half * half;
            else
                return half * half * x;
        }
    }

    二刷:

    class Solution {
        public double myPow(double x, int n) {
            if (n < 0) {
                return 1 / helper(x, -n);
            }
            return helper(x, n);
        }
        
        private double helper(double x, int n) {
            if (n == 0) {
                return 1;
            }
            double half = helper(x, n / 2);
            return n % 2 == 0 ? half * half : half * half * x;
        }
    }
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  • 原文地址:https://www.cnblogs.com/fatttcat/p/10063593.html
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