LeetCode in Kotlin

1138. Alphabet Board Path

Medium

On an alphabet board, we start at position (0, 0), corresponding to character board[0][0].

Here, board = ["abcde", "fghij", "klmno", "pqrst", "uvwxy", "z"], as shown in the diagram below.

We may make the following moves:

• 'U' moves our position up one row, if the position exists on the board;
• 'D' moves our position down one row, if the position exists on the board;
• 'L' moves our position left one column, if the position exists on the board;
• 'R' moves our position right one column, if the position exists on the board;
• '!' adds the character board[r][c] at our current position (r, c) to the answer.

(Here, the only positions that exist on the board are positions with letters on them.)

Return a sequence of moves that makes our answer equal to target in the minimum number of moves. You may return any path that does so.

Example 1:

Input: target = “leet”

Output: “DDR!UURRR!!DDD!”

Example 2:

Input: target = “code”

Output: “RR!DDRR!UUL!R!”

Constraints:

• 1 <= target.length <= 100
• target consists only of English lowercase letters.

Solution

class Solution {
    fun alphabetBoardPath(target: String): String {
        if (target.isEmpty()) {
            return ""
        }
        var sourceRow = 0
        var sourceCol = 0
        val path = StringBuilder()
        for (c in target.toCharArray()) {
            val position = c.code - 97
            val targetRow = position / 5
            val targetCol = position % 5
            if (targetCol < sourceCol) {
                path.append(helper("L", sourceCol - targetCol))
            }
            if (targetRow < sourceRow) {
                path.append(helper("U", sourceRow - targetRow))
            }
            if (targetRow > sourceRow) {
                path.append(helper("D", targetRow - sourceRow))
            }
            if (targetCol > sourceCol) {
                path.append(helper("R", targetCol - sourceCol))
            }
            path.append("!")
            sourceRow = targetRow
            sourceCol = targetCol
        }
        return path.toString()
    }

    fun helper(dir: String?, time: Int): StringBuilder {
        val path = StringBuilder()
        for (i in 0 until time) {
            path.append(dir)
        }
        return path
    }
}

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