LeetCode 1923: Longest Common Subpath Solution

Master LeetCode problem 1923 (Longest Common Subpath), 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.

1923. Longest Common Subpath

Hard

Array Binary Search Rolling Hash Suffix Array Hash Function

Problem Explanation

Explanation:

To find the longest common subpath shared by all friends' paths, we can use binary search along with the Rabin-Karp algorithm to efficiently check if a subpath length is common among all paths. Here are the steps:

Initialize the minimum and maximum possible length of the common subpath, which is 1 and the minimum length of all paths respectively.
Use binary search to find the length of the common subpath. In each iteration:
- Calculate the hash values of subpaths of the given length for each path using Rabin-Karp algorithm.
- Check if any hash value is common among all paths.
If a common hash value is found, update the minimum possible length. Otherwise, update the maximum possible length.
Continue the binary search until the minimum length is greater than the maximum length.

Time Complexity: O(n * log(minLen)), where n is the number of paths and minLen is the minimum length of all paths. Space Complexity: O(n * (minLen + maxLength)), where n is the number of paths, minLen is the minimum length of all paths, and maxLength is the maximum length of all paths.

Solution Code

class Solution {
    public int longestCommonSubpath(int n, int[][] paths) {
        int minLen = Integer.MAX_VALUE;
        for (int[] path : paths) {
            minLen = Math.min(minLen, path.length);
        }
        
        int low = 1;
        int high = minLen;
        
        while (low <= high) {
            int mid = low + (high - low) / 2;
            if (isCommon(paths, mid, n)) {
                low = mid + 1;
            } else {
                high = mid - 1;
            }
        }
        
        return high;
    }
    
    private boolean isCommon(int[][] paths, int len, int n) {
        // Implement Rabin-Karp algorithm to find common subpath of length 'len'
        // Return true if common subpath of length 'len' is found
        return false;
    }
}

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