LeetCode-in-Java
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.ArrayList;
import java.util.List;
public class Solution {
private List<String> ans = new ArrayList<>();
public List<String> letterCasePermutation(String s) {
helper(s, 0, "");
return ans;
}
public void helper(String s, int curr, String temp) {
if (curr == s.length()) {
ans.add(temp);
return;
}
if (Character.isDigit(s.charAt(curr))) {
helper(s, curr + 1, temp + s.charAt(curr));
} else {
if (Character.isLowerCase(s.charAt(curr))) {
helper(s, curr + 1, temp + s.charAt(curr));
helper(s, curr + 1, temp + (s.substring(curr, curr + 1)).toUpperCase());
} else {
helper(s, curr + 1, temp + s.charAt(curr));
helper(s, curr + 1, temp + (s.substring(curr, curr + 1)).toLowerCase());
}
}
}
}