max69.js

// 1323. Maximum 69 Number
// Easy

// Given a positive integer num consisting only of digits 6 and 9.

// Return the maximum number you can get by changing at most one digit(6 becomes 9, and 9 becomes 6).

//     Example 1:

// Input: num = 9669
// Output: 9969
// Explanation:
// Changing the first digit results in 6669.
// Changing the second digit results in 9969.
// Changing the third digit results in 9699.
// Changing the fourth digit results in 9666.
// The maximum number is 9969.
// Example 2:

// Input: num = 9996
// Output: 9999
// Explanation: Changing the last digit 6 to 9 results in the maximum number.
//     Example 3:

// Input: num = 9999
// Output: 9999
// Explanation: It is better not to apply any change.

//     Constraints:

// 1 <= num <= 10 ^ 4
// num's digits are 6 or 9.

// source: https://leetcode.com/problems/maximum-69-number/

/**
 * @param {number} num
 * @return {number}
 */
var maximum69Number = function(num) {
  const nums = num.toString().split("");

  for (number in nums) {
    if (nums[number] == "6") {
      nums[number] = "9";
      break;
    }
  }
  return parseInt(nums.join(""));
};

// alternate solution with built-ins which takes more time:
// return parseInt(num.toString().replace("6", "9"))