add 784

fishercoder1534 · fishercoder1534 · commit dfaae983877f · 2018-02-18T08:45:48.000-08:00
diff --git a/README.md b/README.md
@@ -22,6 +22,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Video  | Difficulty  | Tag                   
 |-----|----------------|---------------|---------------|---------------|--------|-------------|-------------
+|784|[Letter Case Permutation](https://leetcode.com/problems/letter-case-permutation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_784.java) | O(n*2^n) | O(n*2^n) | |Easy|
 |783|[Minimum Distance Between BST Nodes](https://leetcode.com/problems/minimum-distance-between-bst-nodes/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_783.java) | O(n) | O(h) | |Easy|
 |779|[K-th Symbol in Grammar](https://leetcode.com/problems/k-th-symbol-in-grammar/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_779.java) | O(logn) | O(1) | |Medium|
 |776|[Split BST](https://leetcode.com/problems/split-bst/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_776.java) | O(n) | O(n) | |Medium| Recursion
diff --git a/src/main/java/com/fishercoder/solutions/_784.java b/src/main/java/com/fishercoder/solutions/_784.java
@@ -0,0 +1,68 @@
+package com.fishercoder.solutions;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * 784. 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.
+
+ Examples:
+ Input: S = "a1b2"
+ Output: ["a1b2", "a1B2", "A1b2", "A1B2"]
+
+ Input: S = "3z4"
+ Output: ["3z4", "3Z4"]
+
+ Input: S = "12345"
+ Output: ["12345"]
+
+ Note:
+
+ S will be a string with length at most 12.
+ S will consist only of letters or digits.
+
+ */
+
+public class _784 {
+  public static class Solution1 {
+    public List<String> letterCasePermutation(String S) {
+      Set<String> result = new HashSet<>();
+      result.add(S);
+      for (int i = 0; i < S.length(); i++) {
+        if (Character.isAlphabetic(S.charAt(i))) {
+          Set<String> newResult = new HashSet<>();
+          for (String word : result) {
+            if (Character.isUpperCase(word.charAt(i))) {
+              StringBuilder sb = new StringBuilder();
+              for (int j = 0; j < i; j++) {
+                sb.append(word.charAt(j));
+              }
+              sb.append(Character.toLowerCase(word.charAt(i)));
+              for (int j = i + 1; j < word.length(); j++) {
+                sb.append(word.charAt(j));
+              }
+              newResult.add(sb.toString());
+            } else {
+              StringBuilder sb = new StringBuilder();
+              for (int j = 0; j < i; j++) {
+                sb.append(word.charAt(j));
+              }
+              sb.append(Character.toUpperCase(word.charAt(i)));
+              for (int j = i + 1; j < word.length(); j++) {
+                sb.append(word.charAt(j));
+              }
+              newResult.add(sb.toString());
+            }
+          }
+          result.addAll(newResult);
+        }
+      }
+      return new ArrayList<>(result);
+    }
+  }
+}
diff --git a/src/test/java/com/fishercoder/_784Test.java b/src/test/java/com/fishercoder/_784Test.java
@@ -0,0 +1,37 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._784;
+import java.util.Arrays;
+import java.util.List;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _784Test {
+  private static _784.Solution1 solution1;
+  private static List<String> expected;
+
+  @BeforeClass
+  public static void setup() {
+    solution1 = new _784.Solution1();
+  }
+
+  @Test
+  public void test1() {
+    expected = Arrays.asList("a1b2", "a1B2", "A1b2", "A1B2");
+    assertEquals(expected, solution1.letterCasePermutation("a1b2"));
+  }
+
+  @Test
+  public void test2() {
+    expected = Arrays.asList("3z4", "3Z4");
+    assertEquals(expected, solution1.letterCasePermutation("3z4"));
+  }
+
+  @Test
+  public void test3() {
+    expected = Arrays.asList("12345");
+    assertEquals(expected, solution1.letterCasePermutation("12345"));
+  }
+}
