Formatted question description: https://leetcode.ca/all/1432.html

# 1432. Max Difference You Can Get From Changing an Integer

Medium

## Description

You are given an integer num. You will apply the following steps exactly two times:

• Pick a digit x (0 <= x <= 9).
• Pick another digit y (0 <= y <= 9). The digit y can be equal to x.
• Replace all the occurrences of x in the decimal representation of num by y.
• The new integer cannot have any leading zeros, also the new integer cannot be 0.

Let a and b be the results of applying the operations to num the first and second times, respectively.

Return the max difference between a and b.

Example 1:

Input: num = 555

Output: 888

Explanation: The first time pick x = 5 and y = 9 and store the new integer in a.

The second time pick x = 5 and y = 1 and store the new integer in b.

We have now a = 999 and b = 111 and max difference = 888

Example 2:

Input: num = 9

Output: 8

Explanation: The first time pick x = 9 and y = 9 and store the new integer in a.

The second time pick x = 9 and y = 1 and store the new integer in b.

We have now a = 9 and b = 1 and max difference = 8

Example 3:

Input: num = 123456

Output: 820000

Example 4:

Input: num = 10000

Output: 80000

Example 5:

Input: num = 9288

Output: 8700

Constraints:

• 1 <= num <= 10^8

## Solution

Obviously, a is the maximum possible integer and b is the minimum possible integer.

To obtain a, find the highest digit that is not 9, and replace all the digits with the value to 9.

To obtain b, consider two cases.

1. If the highest digit is 1, then find the highest digit that is not 0 or 1, and replace all the digits with the value to 0. Note that the original digit cannot have value 1 since the highest digit cannot be changed to 0.
2. If the nighest digit is not 1, then simply replace all the digits with the same value as the highest digit to 1.

After obtaining a and b, return a - b.

class Solution {
public int maxDiff(int num) {
int max = getMax(num), min = getMin(num);
return max - min;
}

public int getMax(int num) {
char[] array = String.valueOf(num).toCharArray();
int length = array.length;
char original = '0';
for (int i = 0; i < length; i++) {
if (array[i] != '9') {
original = array[i];
break;
}
}
for (int i = 0; i < length; i++) {
if (array[i] == original)
array[i] = '9';
}
return Integer.parseInt(new String(array));
}

public int getMin(int num) {
char[] array = String.valueOf(num).toCharArray();
int length = array.length;
if (array == '1') {
char original = '0';
for (int i = 1; i < length; i++) {
if (array[i] != '0' && array[i] != '1') {
original = array[i];
break;
}
}
for (int i = 1; i < length; i++) {
if (array[i] == original)
array[i] = '0';
}
} else {
char original = array;
for (int i = 0; i < length; i++) {
if (array[i] == original)
array[i] = '1';
}
}
return Integer.parseInt(new String(array));
}
}