2443. Sum of Number and Its Reverse

Problem

Given a non-negative integer num, return true if num can be expressed as the sum of any non-negative integer and its reverse, or false otherwise.

Example 1:

Input: num = 443
Output: true
Explanation: 172 + 271 = 443 so we return true.

Example 2:

Input: num = 63
Output: false
Explanation: 63 cannot be expressed as the sum of a non-negative integer and its reverse so we return false.

Example 3:

Input: num = 181
Output: true
Explanation: 140 + 041 = 181 so we return true. Note that when a number is reversed, there may be leading zeros.

Constraints:

• 0 <= num <= 10^5

Solution (Java)

class Solution {
    static HashSet<Integer> set = new HashSet<>();
    static {
        for(int i=0;i<=100000;i++){
            set.add(i+Integer.parseInt(new StringBuilder(Integer.toString(i)).reverse().toString()));
        }
    }
    public boolean sumOfNumberAndReverse(int num) {
        return set.contains(num);
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).