Largest 3-Same-Digit Number in String

You are given a string num representing a large integer. An integer is good if it meets the following conditions:

• It is a substring of num with length 3.

• It consists of only one unique digit.

Return the maximum good integer as a string or an empty string "" if no such integer exists.

Note:

• A substring is a contiguous sequence of characters within a string.

• There may be leading zeroes in num or a good integer.

LeetCode Problem - 2264

class Solution {
    // Method to find the largest good integer substring in a given string
    public String largestGoodInteger(String num) {
        // Initialize a flag to keep track of the largest good integer found
        int flag = Integer.MIN_VALUE;

        // Iterate through the string, considering each possible substring of length 3
        for(int i = 0; i < num.length() - 2; i++) {
            // Extract the three digits of the current substring
            int check = num.charAt(i) - '0', a = num.charAt(i + 1) - '0', b = num.charAt(i + 2) - '0';
            // Calculate the integer value of the current substring
            int substring = (check * 100) + (a * 10) + b;
            // Check if all three digits are equal
            if(check == a && check == b) {
                // If the current substring is greater than the current flag, update the flag
                if(substring > flag) {
                    flag = substring;
                }
            }
        }

        // If no good integer is found, return "000"
        if(flag == 0) {
            return "000";
        }

        // If the flag remains negative, return an empty string; otherwise, return the flag as a string
        return flag < 0 ? "" : String.valueOf(flag);
    }
}