LeetCode 3090: Maximum Length Substring With Two Occurrences Solution

Master LeetCode problem 3090 (Maximum Length Substring With Two Occurrences), a easy challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

3090. Maximum Length Substring With Two Occurrences

Easy

Hash Table String Sliding Window

Problem Explanation

Explanation

To solve this problem, we can use a sliding window approach. We will maintain a hashmap to keep track of the frequency of characters in the current window. We will also keep track of the start and end indices of the window. As we iterate through the string, we will expand the window until we have at most two occurrences of each character. If we encounter a character that violates this condition, we will shrink the window from the left side until the condition is satisfied again. At each step, we will update the maximum length of the valid substring.

Time complexity: O(n) where n is the length of the input string s. Space complexity: O(1) since the hashmap will have at most 26 entries for lowercase English letters.

Solution Code

class Solution {
    public int maxLengthTwoOccurrences(String s) {
        int[] freq = new int[26];
        int start = 0, end = 0;
        int maxLen = 0;
        
        while (end < s.length()) {
            freq[s.charAt(end) - 'a']++;
            
            while (countOccurences(freq) > 2) {
                freq[s.charAt(start) - 'a']--;
                start++;
            }
            
            maxLen = Math.max(maxLen, end - start + 1);
            end++;
        }
        
        return maxLen;
    }
    
    private int countOccurences(int[] freq) {
        int count = 0;
        for (int i = 0; i < 26; i++) {
            if (freq[i] > 0) {
                count++;
            }
        }
        return count;
    }
}

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