package LeetCode_784
/**
* 784. Letter Case Permutation
* https://leetcode.com/problems/letter-case-permutation/
* Given a string S, we can transform every letter individually to be lowercase or uppercase to create another string.
Return a list of all possible strings we could create. You can return the output in any order.
Example 1:
Input: S = "a1b2"
Output: ["a1b2","a1B2","A1b2","A1B2"]
Example 2:
Input: S = "3z4"
Output: ["3z4","3Z4"]
Example 3:
Input: S = "12345"
Output: ["12345"]
Example 4:
Input: S = "0"
Output: ["0"]
Constraints:
1. S will be a string with length between 1 and 12.
2. S will consist only of letters or digits.
* */
class Solution {
/*
* solution: dfs + backtracking, Time:O(2^n), Space:O(2^n)
* */
fun letterCasePermutation(S: String): List<String> {
val result = ArrayList<String>()
if (S == null || S.isEmpty()) {
return result
}
dfs(0, S.toCharArray(), result)
return result
}
private fun dfs(pos: Int, chars: CharArray, result: ArrayList<String>) {
if (pos == chars.size) {
result.add(String(chars))
return
}
if (chars[pos].isDigit()) {
//if digit, check next char
return dfs(pos + 1, chars, result)
}
//change current pos to lower case
chars[pos] = chars[pos].toLowerCase()
//and keep tracking via next level
dfs(pos + 1, chars, result)
//change current pos to upper case
chars[pos] = chars[pos].toUpperCase()
//and keep tracking via next level
dfs(pos + 1, chars, result)
}
}
