# 7.Reverse Integer <span class='tag' data-diff="easy"></span>
{%hackmd RN5D4nggQRO8wzNqxuvlNw %}

## 題目
Given a 32-bit signed integer, reverse digits of an integer.

**Example 1:**

Input: 123
Output: 321

**Example 2:**

Input: -123
Output: -321

**Example 3:**

Input: 120
Output: 21

Note:
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: $[−2^{31}, 2^{31} − 1]$. For the purpose of this problem, assume that your function returns 0 when the reversed integer overflows.

## 思路

var reverse = function(x) {
    let sign = x < 0 ? -1 : 1;
    let value = sign * Number(Math.abs(x).toString().split("").reverse().join(""));
    if(value > 2**31 - 1 || value < -1 * 2**31 ) value = 0;
    return value ;
};

這一題真的很簡單，只要轉成字串、反轉再轉回Int即可，但要注意題目中有特別針對overflow的情況要求回傳值，由於javascript中Number物件是以IEEE 754中規範的64bit雙精度浮點數來儲存的，範圍可以到 $[-(2^{53}-1), (2^{53}-1)]$ ，所以需要主動判斷是否有溢位。