LeetCode 3501: Maximize Active Section with Trade II Solution

Master LeetCode problem 3501 (Maximize Active Section with Trade II), a hard 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.

3501. Maximize Active Section with Trade II

Hard

Array String Binary Search Segment Tree

Problem Explanation

Explanation:

To solve this problem, we need to find the maximum number of active sections in a given substring after performing at most one trade. We can achieve this by iterating through each query and applying the trade operation if possible.

For each query [li, ri], we augment the substring with '1' at both ends.
We then check if there is a contiguous block of '1's surrounded by '0's. If found, we convert that block to '0's.
Next, we check if there is a contiguous block of '0's surrounded by '1's. If found, we convert that block to '1's.
Finally, we count the number of active sections in the resulting substring and store it as the answer for the query.

Solution Code

class Solution {
    public int[] maximizeActiveSections(String s, int[][] queries) {
        int n = s.length();
        int[] answer = new int[queries.length];
        
        for (int i = 0; i < queries.length; i++) {
            int li = queries[i][0];
            int ri = queries[i][1];
            
            String augmented = "1" + s.substring(li, ri + 1) + "1";
            int activeSections = 0;
            
            for (int j = 1; j < augmented.length() - 1; j++) {
                if (augmented.charAt(j) == '1' && augmented.charAt(j - 1) == '0' && augmented.charAt(j + 1) == '0') {
                    activeSections++;
                    j++;
                }
            }
            
            answer[i] = activeSections;
        }
        
        return answer;
    }
}

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