main.go

// Source: https://leetcode.com/problems/max-difference-you-can-get-from-changing-an-integer
// Title: Max Difference You Can Get From Changing an Integer
// Difficulty: Medium
// Author: Mu Yang <http://muyang.pro>

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// You are given an integer `num`. You will apply the following steps to `num` **two** separate times:
//
// - Pick a digit `x (0 <= x <= 9)`.
// - Pick another digit `y (0 <= y <= 9)`. Note `y` can be equal to `x`.
// - Replace all the occurrences of `x` in the decimal representation of `num` by `y`.
//
// Let `a` and `b` be the two results from applying the operation to `num` independently.
//
// Return the max difference between `a` and `b`.
//
// Note that neither `a` nor `b` may have any leading zeros, and **must not** be 0.
//
// **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
// ```
//
// **Constraints:**
//
// - `1 <= num <= 10^8`
//
////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

package main

import (
	"strconv"
	"strings"
)

// To maximize the number, remap to hightest non-9 digit to 9.
// To minimize the number,
// * if the hightest digit is not 1, remap all that digit to 1
// * otherwise, remap th highest non-0 & non-1 digit to 0
func maxDiff(num int) int {
	digits := strconv.Itoa(num)

	// Maximize
	maxDigit := '9'
	for _, digit := range digits {
		if digit != '9' {
			maxDigit = digit
			break
		}
	}
	maxDigits := digits
	if maxDigit != '9' {
		maxDigits = strings.ReplaceAll(digits, string(maxDigit), "9")
	}
	maxNum, _ := strconv.Atoi(maxDigits)

	// Minimize
	minDigits := digits
	if digits[0] != '1' {
		minDigits = strings.ReplaceAll(digits, string(digits[0]), "1")
	} else {
		minDigit := '0'
		for _, digit := range digits {
			if digit != '0' && digit != '1' {
				minDigit = digit
				break
			}
		}
		if minDigit != '0' && minDigit != '1' {
			minDigits = strings.ReplaceAll(digits, string(minDigit), "0")
		}
	}
	minNum, _ := strconv.Atoi(minDigits)

	return maxNum - minNum
}