7. Reverse Integer

Description

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

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.

Constraints

Approach

Links

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

Example 1

Input: 123

Output: 321

Example 2

Input: -123

Output: -321

Example 3

Input: 120

Output: 21

Solutions

Solution 1

/**
 * Time complexity : O(log(x)). There are roughly log10(x) digits in x.
 * Space complexity : O(1)
 */

class Solution {
    public int reverse(int x) {
        int n = 0, flag = (x < 0)? -1: 1;
        x *= flag;
        while(x > 0) {
            int pop = x%10;
            if(n > Integer.MAX_VALUE/10 || 
               (n == Integer.MAX_VALUE/10 && pop > 2)) return 0;
            n = (n*10) + pop;
            x /= 10;
        }
        return n * flag;
    }
}

Follow up