LeetCode in Kotlin
784. Letter Case Permutation
Medium
Given a string s, you can transform every letter individually to be lowercase or uppercase to create another string.
Return a list of all possible strings we could create. Return the output in any order.
Example 1:
Input: s = “a1b2”
Output: [“a1b2”,”a1B2”,”A1b2”,”A1B2”]
Example 2:
Input: s = “3z4”
Output: [“3z4”,”3Z4”]
Constraints:
1 <= s.length <= 12sconsists of lowercase English letters, uppercase English letters, and digits.
Solution
import java.util.Locale
class Solution {
private val ans: MutableList<String> = ArrayList()
fun letterCasePermutation(s: String): List<String> {
helper(s, 0, "")
return ans
}
private fun helper(s: String, curr: Int, temp: String) {
if (curr == s.length) {
ans.add(temp)
return
}
if (Character.isDigit(s[curr])) {
helper(s, curr + 1, temp + s[curr])
} else {
if (Character.isLowerCase(s[curr])) {
helper(s, curr + 1, temp + s[curr])
helper(s, curr + 1, temp + s.substring(curr, curr + 1).uppercase(Locale.getDefault()))
} else {
helper(s, curr + 1, temp + s[curr])
helper(s, curr + 1, temp + s.substring(curr, curr + 1).lowercase(Locale.getDefault()))
}
}
}
}