2264. Largest 3-Same-Digit Number in String

Description

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.

 

Solutions

Solution: Brute Force

• Time complexity: O(n)
• Space complexity: O(1)

 

JavaScript

/**
 * @param {string} num
 * @return {string}
 */
const largestGoodInteger = function (num) {
  const n = num.length;
  let maxGood = -1;
  let result = '';

  for (let index = 1; index < n; index++) {
    const str = num[index];

    if (str !== num[index - 1] || str !== num[index - 2]) {
      continue;
    }
    const integer = str.repeat(3);

    if (Number(integer) > maxGood) {
      result = integer;
      maxGood = Number(integer);
    }
  }

  return result;
};