2981. Find Longest Special Substring That Occurs Thrice I

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2981. Find Longest Special Substring That Occurs Thrice I

Description

You are given a string s that consists of lowercase English letters.

A string is called special if it is made up of only a single character. For example, the string "abc" is not special, whereas the strings "ddd", "zz", and "f" are special.

Return the length of the longest special substring of s which occurs at least thrice , or -1 if no special substring occurs at least thrice.

A substring is a contiguous non-empty sequence of characters within a string.

Example 1:

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Input: s = "aaaa"
Output: 2
Explanation: The longest special substring which occurs thrice is "aa": substrings "**aa** aa", "a**aa** a", and "aa**aa** ".
It can be shown that the maximum length achievable is 2.

Example 2:

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Input: s = "abcdef"
Output: -1
Explanation: There exists no special substring which occurs at least thrice. Hence return -1.

Example 3:

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Input: s = "abcaba"
Output: 1
Explanation: The longest special substring which occurs thrice is "a": substrings "**a** bcaba", "abc**a** ba", and "abcab**a** ".
It can be shown that the maximum length achievable is 1.

Constraints:

  • 3 <= s.length <= 50
  • s consists of only lowercase English letters.

Hints/Notes

Solution

Language: C++

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class Solution {
public:
    int maximumLength(string s) {
        unordered_map<string, int> m;
        int n = s.size(), res = -1;
        for (int i = 0; i < n; ) {
            int start = i;
            while (s[i] == s[start]) {
                i++;
            }
            int len = i - start;
            string cur = s.substr(start, len);
            m[cur]++;
            if (m[cur] >= 3) res = max(res, (int)cur.size());
            cur.pop_back();
            if (!cur.empty()) {
                m[cur] += 2;
                if (m[cur] >= 3) {
                    res = max(res, (int)cur.size());
                }
                cur.pop_back();
                if (!cur.empty()) {
                    res = max(res, (int)cur.size());
                }
            }
        }
        return res;
    }
};