Create LetterCasePermutation.java

Author: 17tanya

Backtracking/LetterCasePermutation.java

@@ -0,0 +1,31 @@
+//LeetCode 784. Letter Case Permutation
+//Question - https://leetcode.com/problems/letter-case-permutation/
+
+class Solution {
+    public List<String> letterCasePermutation(String S) {
+        List<String> res = new ArrayList<>();
+        helper(S, "", 0, res);
+        return res;
+    }
+    
+    public void helper(String inputString, String newString, int index, List<String> l){
+        //base condition
+        if(inputString.length() == newString.length()){
+            l.add(newString);
+            return;
+        }
+        
+        //check if current char is a number or alphabet
+        char currChar = inputString.charAt(index);
+        if(Character.isDigit(currChar)){
+            helper(inputString, newString + currChar, index + 1, l);
+        }
+        else{
+            //considering lower case 
+            helper(inputString, newString + Character.toLowerCase(currChar), index + 1, l);
+            
+            //considering upper case
+            helper(inputString, newString + Character.toUpperCase(currChar), index + 1, l);
+        }
+    }
+}