LeetCode 9. Palindrome Number

LeetCode problem No.9.

No.8 is here.

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9. Palindrome Number

https://leetcode.com/problems/palindrome-number/

Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.

Example 1

Input: 121
Output: true

Example 2

Input: -121
Output: false

Example 3

Input: 10
Output: false

Code

object Solution {
    def isPalindrome(x: Int): Boolean = {
        val str = x.toString
        str == str.reverse
    }
}

Methods

• Convert integer to string.
• Make reversed string.
• Compare string and reversed string.

Result

Runtime: 512 ms, faster than 6.09% of Scala online submissions for Palindrome Number. Memory Usage: 55 MB, less than 100.00% of Scala online submissions for Palindrome Number.

Follow up

Coud you solve it without converting the integer to a string?

Code

object Solution {
    def isPalindrome(x: Int): Boolean = {
        if(x < 0 || (x%10 == 0 && x != 0)) false
        else {
          var num = x
          var reversed = 0
          while(num > reversed) {
            reversed = reversed*10 + num%10
            num = num/10
          }
          num == reversed || num == reversed/10
        }
    }
}

Methods

• Initial num is x.
• Initial reversed num is 0.
• Calculate reversed num while reversed num is smaller than num.
  • Multiply reversed num by 10 and add remainder of num.
  • Divide num by 10.
• If num is equal to reversed num, true.
• if num is equal to reversed num divided by 10, true.

Result

Runtime: 904 ms, faster than 6.09% of Scala online submissions for Palindrome Number. Memory Usage: 54.6 MB, less than 100.00% of Scala online submissions for Palindrome Number.