Javascript(leetcode#50) Pow(x, n)

Difficult:Medium

題目

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

翻譯

實現 pow(x, n)，它計算 x 的 n 次冪（即 xn）。

範例

Example 1:

Input: x = 2.00000, n = 10
Output: 1024.00000

Example 2:

Input: x = 2.10000, n = 3
Output: 9.26100

Example 3:

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

解題思路

1.利用遞迴將問題猜解
2.若為偶數不需乘X

Solution

Code 1 :

var myPow = function(x, n) {
  if(n<0){
    return power(1/x,-n);
  }else{
    return power(x,n);
  }
};

function power(x, y){
  if (y === 0) {
    return 1;
  }
  var yBy2 = y / 2;
  var pow = power(x, parseInt( yBy2, 10) );
  if (y % 2 === 0) {
    return pow * pow;
  } else {
    return x * pow * pow;
  }
}