2264. Largest 3-Same-Digit Number in String

Problem

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.

  Example 1:

Input: num = "6777133339"
Output: "777"
Explanation: There are two distinct good integers: "777" and "333".
"777" is the largest, so we return "777".

Example 2:

Input: num = "2300019"
Output: "000"
Explanation: "000" is the only good integer.

Example 3:

Input: num = "42352338"
Output: ""
Explanation: No substring of length 3 consists of only one unique digit. Therefore, there are no good integers.

  Constraints:

• 3 <= num.length <= 1000

• num only consists of digits.

Solution (Java)

class Solution {
    public String largestGoodInteger(String num) {
        String maxi = "000";
        int c = 0;
        for (int i = 0; i < num.length() - 2; i++) {
            String s = num.substring(i, i + 3);
            if (s.charAt(0) == s.charAt(1) && s.charAt(1) == s.charAt(2)) {
                if (s.compareTo(maxi) >= 0) {
                    maxi = s;
                }
                ++c;
            }
        }
        if (c == 0) {
            return "";
        }
        return maxi;
    }
}

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).