2566. Maximum Difference by Remapping a Digit

Time: O(d)

Space: O(d)

Intuition

Maximum difference by changing one digit. To maximize: increase leftmost non-9 digit to 9. Decrease: if first digit > 1 set to 1, else find first non-0/1 and set to 0.

Algorithm

1Max: replace first non-9 digit with 9.
2Min: if first digit != 1: replace all first-digit with 1. Else: replace first non-0/1 with 0.

Common Pitfalls

•Min must not create leading zeros. Special case for first digit.

2566.cs

// Approach: Max: replace first digit with 9; Min: replace first non-9 digit with 0 (or 1st digit→0).
// Time: O(d) Space: O(d)

public class Solution
{
    public int MinMaxDifference(int num)
    {
        string numStr = num.ToString(); // Convert the integer to a string for manipulation
        int minVal = int.Parse(numStr.Replace(numStr[0], '0')); // Replace first digit with '0' to get the minimum value
        // Iterate over the characters in the string
        foreach (char digit in numStr)
        {
            if (digit != '9')
                // Replace the current digit with '9' to get the maximum value and return the difference
                return int.Parse(numStr.Replace(digit, '9')) - minVal;
        }
        // If all digits are '9', return the difference between the original number and minVal
        return num - minVal;
    }
}

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