「前端刷题」9. 回文数

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leetcode-cn站点挂了，用原站吧。

题目

Given an integer x, return true if x is palindrome integer.

An integer is a palindrome when it reads the same backward as forward. For example, 121 is palindrome while 123 is not.

 

Example 1:

Input: x = 121

Output: true

Example 2:

Input: x = -121

Output: false

Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.

Example 3:

Input: x = 10

Output: false

Explanation: Reads 01 from right to left. Therefore it is not a palindrome.

Example 4:

Input: x = -101

Output: false

 

Constraints:

• -231 <= x <= 231 - 1

 

Follow up: Could you solve it without converting the integer to a string?

解题思路

思路1

Use a varibale to reverse number then check with given number

var isPalindrome = function(x) {
  if (x < 0) return false

  let rev = 0
  for(let i = x; i >= 1; i = Math.floor(i/10)) rev = rev*10 + i%10
  return rev === x
};

思路2

var isPalindrome = function(x) {
    const arr = String(x).split('');
        
    while (arr.length > 1) {
        if (arr.shift() !== arr.pop()) {
            return false;
        }
    }
    
    return true;
};

思路3

var isPalindrome = function(x) {
    if (x < 0) return false;
	
    // reverse the string representation of x
    const reverse = `${x}`.split('').reverse().join('');
    // compare the value regardless of types
    return x == reverse;
};

最后

曾梦想仗剑走天涯

看一看世界的繁华

年少的心总有些轻狂

终究不过是个普通人

无怨无悔我走我路

「前端刷题」No.9