LeetCode in Kotlin

777. Swap Adjacent in LR String

Medium

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 end, return True if and only if there exists a sequence of moves to transform one string to the other.

Example 1:

Input: start = “RXXLRXRXL”, end = “XRLXXRRLX”

Output: true

Explanation: We can transform start to end following these steps:

RXXLRXRXL ->

XRXLRXRXL ->

XRLXRXRXL ->

XRLXXRRXL ->

XRLXXRRLX

Example 2:

Input: start = “X”, end = “L”

Output: false

Constraints:

• 1 <= start.length <= 104
• start.length == end.length
• Both start and end will only consist of characters in 'L', 'R', and 'X'.

Solution

class Solution {
    fun canTransform(start: String, end: String): Boolean {
        var i1 = 0
        var i2 = 0
        val s1 = start.toCharArray()
        val s2 = end.toCharArray()
        while (i1 < s1.size && i2 < s2.size) {
            while (i1 < s1.size && s1[i1] == 'X') {
                i1++
            }
            while (i2 < s2.size && s2[i2] == 'X') {
                i2++
            }
            if (i1 == s1.size && i2 == s2.size) {
                return true
            }
            if (i1 == s1.size || i2 == s2.size) {
                return false
            }
            val c1 = s1[i1]
            val c2 = s2[i2]
            if (c1 != c2) {
                return false
            }
            if (c1 == 'L' && i1 < i2) {
                return false
            }
            if (c1 == 'R' && i1 > i2) {
                return false
            }
            i1++
            i2++
        }
        while (i1 < s1.size && start[i1] == 'X') {
            i1++
        }
        while (i2 < s2.size && end[i2] == 'X') {
            i2++
        }
        return i1 == s1.size && i2 == s2.size
    }
}

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