LeetCode in Kotlin

936. Stamping The Sequence

Hard

You are given two strings stamp and target. Initially, there is a string s of length target.length with all s[i] == '?'.

In one turn, you can place stamp over s and replace every letter in the s with the corresponding letter from stamp.

• For example, if stamp = "abc" and target = "abcba", then s is "?????" initially. In one turn you can:

  • place stamp at index 0 of s to obtain "abc??",
  • place stamp at index 1 of s to obtain "?abc?", or
  • place stamp at index 2 of s to obtain "??abc".

  Note that stamp must be fully contained in the boundaries of s in order to stamp (i.e., you cannot place stamp at index 3 of s).

We want to convert s to target using at most 10 * target.length turns.

Return an array of the index of the left-most letter being stamped at each turn. If we cannot obtain target from s within 10 * target.length turns, return an empty array.

Example 1:

Input: stamp = “abc”, target = “ababc”

Output: [0,2]

Explanation: Initially s = “?????”.

• Place stamp at index 0 to get “abc??”.

• Place stamp at index 2 to get “ababc”.

[1,0,2] would also be accepted as an answer, as well as some other answers.

Example 2:

Input: stamp = “abca”, target = “aabcaca”

Output: [3,0,1]

Explanation: Initially s = “???????”.

• Place stamp at index 3 to get “???abca”.

• Place stamp at index 0 to get “abcabca”.

• Place stamp at index 1 to get “aabcaca”.

Constraints:

• 1 <= stamp.length <= target.length <= 1000
• stamp and target consist of lowercase English letters.

Solution

@Suppress("NAME_SHADOWING")
class Solution {
    fun movesToStamp(stamp: String, target: String): IntArray {
        val moves: MutableList<Int> = ArrayList()
        val s = stamp.toCharArray()
        val t = target.toCharArray()
        var stars = 0
        val visited = BooleanArray(target.length)
        while (stars < target.length) {
            var doneReplace = false
            for (i in 0..target.length - stamp.length) {
                if (!visited[i] && canReplace(t, i, s)) {
                    stars = doReplace(t, i, s, stars)
                    doneReplace = true
                    visited[i] = true
                    moves.add(i)
                    if (stars == t.size) {
                        break
                    }
                }
            }
            if (!doneReplace) {
                return IntArray(0)
            }
        }
        val result = IntArray(moves.size)
        for (i in moves.indices) {
            result[i] = moves[moves.size - i - 1]
        }
        return result
    }

    private fun canReplace(t: CharArray, i: Int, s: CharArray): Boolean {
        for (j in s.indices) {
            if (t[i + j] != '*' && t[i + j] != s[j]) {
                return false
            }
        }
        return true
    }

    private fun doReplace(t: CharArray, i: Int, s: CharArray, stars: Int): Int {
        var stars = stars
        for (j in s.indices) {
            if (t[i + j] != '*') {
                t[i + j] = '*'
                stars++
            }
        }
        return stars
    }
}

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