Leetcode•Nov 12, 2026

Swap Adjacent in LR String

Hazrat Ali

Leetcode

In a string composed of 'L', 'R', and 'X' characters, like "RXXLRXRXL", a move consists of either replacing one occurrence of "XL" with "LX", or replacing one occurrence of "RX" with "XR". Given the starting string start and the ending string result, return True if and only if there exists a sequence of moves to transform start to result.

 

Example 1:

Input: start = "RXXLRXRXL", result = "XRLXXRRLX"
Output: true
Explanation: We can transform start to result following these steps:
RXXLRXRXL ->
XRXLRXRXL ->
XRLXRXRXL ->
XRLXXRRXL ->
XRLXXRRLX

Example 2:

Input: start = "X", result = "L"
Output: false

Solution
var canTransform = function(start, result) {
    if (start.length !== result.length) return false;

    let i = 0;
    let j = 0;
    const n = start.length;

    while (i < n && j < n) {
        while (i < n && start[i] === 'X') i++;
        while (j < n && result[j] === 'X') j++;

        if (i === n || j === n) {
            return i === n && j === n;
        }

        if (start[i] !== result[j]) return false;

        if (start[i] === 'L' && i < j) return false;

        if (start[i] === 'R' && i > j) return false;

        i++;
        j++;
    }

    while (i < n && start[i] === 'X') i++;
    while (j < n && result[j] === 'X') j++;

    return i === n && j === n;
};
 

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