Add 784

Author: ChienkuChen

src/_784/784.letter-case-permutation.java

@@ -0,0 +1,37 @@
+package _784;
+
+import java.util.ArrayList;
+import java.util.List;
+
+class Solution {
+    public List<String> letterCasePermutation(String S) {
+        if (S == null)
+            return new ArrayList<>();
+
+        List<String> result = new ArrayList<>();
+        helper(S, 0, "", result);
+
+        return result;
+    }
+
+    private void helper(String S, int start, String tmp, List<String> result) {
+        if (start >= S.length()) {
+            result.add(tmp);
+            return;
+        }
+
+        helper(S, start + 1, tmp + S.charAt(start), result);
+
+        if (Character.getType(S.charAt(start)) == Character.LOWERCASE_LETTER) {
+            helper(S, start + 1, tmp + Character.toUpperCase(S.charAt(start)), result);
+        } else if (Character.getType(S.charAt(start)) == Character.UPPERCASE_LETTER) {
+            helper(S, start + 1, tmp + Character.toLowerCase(S.charAt(start)), result);
+        }
+    }
+
+    public static void main(String[] args) {
+        System.out.println(new Solution().letterCasePermutation("a1b2"));
+        System.out.println(new Solution().letterCasePermutation("3z4"));
+        System.out.println(new Solution().letterCasePermutation("12345"));
+    }
+}