1903. Largest Odd Number in String

Problem

You are given a string num, representing a large integer. Return **the *largest-valued odd* integer (as a string) that is a non-empty substring of num, or an empty string "" if no odd integer exists**.

A substring is a contiguous sequence of characters within a string.

  Example 1:

Input: num = "52"
Output: "5"
Explanation: The only non-empty substrings are "5", "2", and "52". "5" is the only odd number.

Example 2:

Input: num = "4206"
Output: ""
Explanation: There are no odd numbers in "4206".

Example 3:

Input: num = "35427"
Output: "35427"
Explanation: "35427" is already an odd number.

  Constraints:

• 1 <= num.length <= 105

• num only consists of digits and does not contain any leading zeros.

Solution

/**
 * @param {string} num
 * @return {string}
 */
var largestOddNumber = function(num) {
    var lastNonZeroNumIndex = -1;
    var firstOddNumIndex = -1;
    for (var i = num.length - 1; i >= 0; i--) {
        if (firstOddNumIndex === -1 && (Number(num[i]) % 2)) {
            firstOddNumIndex = i;
        }
        if (num[i] !== '0') {
            lastNonZeroNumIndex = i;
        }
    }
    return firstOddNumIndex === -1
        ? '' :
        num.slice(lastNonZeroNumIndex, firstOddNumIndex + 1)
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(1).