2264. Largest 3-Same-Digit Number in String

Easy

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.

解題

func largestGoodInteger(num string) string {
    ans := ""
    
    for i:=0; i<= len(num)-3; i++ {
        if num[i]==num[i+1] && num[i]==num[i+2] {
            if len(ans)==0 { 
                ans = num[i:i+3] 
            } else {
                if num[i] > ans[0] { 
                    ans = num[i:i+3]  
                }
            }
        }
    }
    
    return ans
}

討論區看到的解法，很優雅，值得學習。

func largestGoodInteger(num string) string {
    max := byte('0'-1)
    for i := 1; i < len(num)-1; i++ {
        if num[i]==num[i+1] && num[i]==num[i-1] && num[i] > max{
            max = num[i]
        }
    }
    if max == byte('0'-1) {
        return ""
    }
    res := []byte{max, max, max}
    return string(res)
}