Maximum Swap

You are given an integer num. You can swap two digits at most once to get the maximum valued number.

Return the maximum valued number you can get.

LeetCode Problem - 670

class Solution {
    public int maximumSwap(int num) {
        // Convert the number to a character array for easy manipulation
        char[] numCharArray = Integer.toString(num).toCharArray();

        boolean flag = true; // Flag to check if any swap has been made
        int idx = -1; // Index of the digit to swap with
        int maxNum = 0; // Maximum digit found for potential swap

        int answer = 0; // Variable to hold the final answer

        // Loop through each digit in the character array
        for(int i = 0; i < numCharArray.length; i++) {
            int currentNum = numCharArray[i] - '0'; // Get the current digit

            // Inner loop to find a larger digit to swap with
            for(int j = i + 1; j < numCharArray.length; j++) {
                int nextBigNum = numCharArray[j] - '0'; // Get the next digit

                // Check if the next digit is larger than the current digit
                // or if we are not in the first swap and it's equal or greater
                if(nextBigNum > currentNum || (!flag && nextBigNum >= currentNum)) {
                    currentNum = nextBigNum; // Update the current number
                    maxNum = nextBigNum; // Track the maximum digit found
                    idx = j; // Update the index of the larger digit
                    flag = false; // Set the flag to indicate a swap has been found
                }
            }

            // If a larger digit was found to swap
            if(!flag) {
                // Swap the digits
                char temp = numCharArray[i];
                numCharArray[i] = numCharArray[idx];
                numCharArray[idx] = temp;   

                // Convert the character array back to an integer
                answer = convertCharArrayToInt(numCharArray);
                break; // Break the loop as we only want the first valid swap
            }
        }

        // If no swap was made, return the original number
        if(flag) return num;
        return answer; // Return the new number after the swap
    }

    // Helper method to convert a character array back to an integer
    public int convertCharArrayToInt(char[] arr) {
        int num = 0; // Initialize the number to 0
        for(char ch : arr) {
            // Build the number by shifting left and adding the new digit
            num = num * 10 + (ch - '0');
        }
        return num; // Return the constructed integer
    }
}