LeetCode 777: Swap Adjacent in LR String Solution

Master LeetCode problem 777 (Swap Adjacent in LR String), a medium 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.

777. Swap Adjacent in LR String

Medium

Two Pointers String

Problem Explanation

Explanation:

We can solve this problem by iterating through the start and result strings in parallel to check if they can be transformed from start to result.
We need to keep track of the positions of 'L' and 'R' in both strings and compare them to see if 'L' in start is always before 'L' in result, and 'R' in start is always after 'R' in result.
We also need to handle 'X' characters in both strings, which can be matched with either 'L' or 'R'.
If at any point the positions do not match the required order, we return false, otherwise, we return true.

Solution Code

class Solution {
    public boolean canTransform(String start, String end) {
        int n = start.length();
        int p1 = 0, p2 = 0;

        while (p1 < n && p2 < n) {
            while (p1 < n && start.charAt(p1) == 'X') p1++;
            while (p2 < n && end.charAt(p2) == 'X') p2++;

            if (p1 == n || p2 == n) {
                return p1 == p2;
            }

            if (start.charAt(p1) != end.charAt(p2) || (start.charAt(p1) == 'L' && p1 < p2) || (start.charAt(p1) == 'R' && p1 > p2)) {
                return false;
            }

            p1++;
            p2++;
        }

        return true;
    }
}

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