替换一个数字后的最大差值

/*
 * Problem Statement:
 * Given an integer num, Danny Mittal will secretly replace one digit (0-9) with another digit (0-9).
 * Return the difference between the maximum value and the minimum value that can be obtained by replacing exactly one digit.
 * 
 * Approach:
 * 1. Convert the number to a string to easily manipulate individual digits.
 * 2. For the maximum value, replace the first non-9 digit with 9.
 * 3. For the minimum value, if the first digit is not 1, replace the first non-0 digit with 0.
 * 4. Calculate the difference between the maximum and minimum values.
 */

import java.util.stream.Collectors;

public class Solution {
    public int maxDifference(int num) {
        String numStr = String.valueOf(num);
        String maxStr = numStr;
        String minStr = numStr;

        // Find maximum value by replacing the first non-9 digit with 9
        maxStr = numStr.chars()
                        .mapToObj(c -> (char) c)
                        .map(c -> c != '9' ? numStr.replace(c, '9') : numStr)
                        .findFirst()
                        .orElse(numStr);

        // Find minimum value by replacing the first non-0 digit with 0
        if (numStr.charAt(0) != '1') {
            minStr = numStr.replace(numStr.charAt(0), '0');
        } else {
            minStr = numStr.chars()
                           .skip(1)
                           .mapToObj(c -> (char) c)
                           .filter(c -> c != '0' && c != '1')
                           .map(c -> numStr.replace(c, '0'))
                           .findFirst()
                           .orElse(numStr);
        }

        int maxNum = Integer.parseInt(maxStr);
        int minNum = Integer.parseInt(minStr);

        return maxNum - minNum;
    }
}