Largest 3-Same-Digit Number in String

2264. 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.

### 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.

Constraints:
3 <= num.length <= 1000
num only consists of digits.

/**
 * @param {string} num
 * @return {string}
 */
var largestGoodInteger = function(num) {
    let str = '', out = '';
    for (let i = 0; i < num.length; i++) {
        str += num[i];
        if (num[i] !== num[i+1]) {
            if (str.length >= 3) {
                str = str.slice(0,3);
                if (+out <= +str) {
                    out = str;
                }
            }

            str = '';
        }
    }  
    return out;  
};