add 859

fishercoder1534 · fishercoder1534 · commit 7aa175a76434 · 2018-12-25T09:40:46.000-08:00
diff --git a/README.md b/README.md
@@ -43,6 +43,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |876|[Middle of the Linked List](https://leetcode.com/problems/middle-of-the-linked-list/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_876.java) | O(n) | O(1) | |Easy|
 |868|[Binary Gap](https://leetcode.com/problems/binary-gap/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_868.java) | O(n) | O(n) | |Easy|
 |867|[Transpose Matrix](https://leetcode.com/problems/transpose-matrix/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_867.java) | O(r*c) | O(r*c) | |Easy|
+|859|[Buddy Strings](https://leetcode.com/problems/buddy-strings/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_859.java) | O(n) | O(n) | |Easy|
 |852|[Peak Index in a Mountain Array](https://leetcode.com/problems/peak-index-in-a-mountain-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_852.java) | O(n) | O(1) | |Easy|
 |844|[Backspace String Compare](https://leetcode.com/problems/backspace-string-compare/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_844.java) | O(n) | O(1) | |Easy|
 |832|[Flipping an Image](https://leetcode.com/problems/flipping-an-image/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_832.java) | O(n) | O(1) | |Easy|
diff --git a/src/main/java/com/fishercoder/solutions/_859.java b/src/main/java/com/fishercoder/solutions/_859.java
@@ -0,0 +1,72 @@
+package com.fishercoder.solutions;
+
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * 859. Buddy Strings
+ *
+ * Given two strings A and B of lowercase letters, return true if and only if we can swap two letters in A so that the result equals B.
+ *
+ *
+ *
+ * Example 1:
+ *
+ * Input: A = "ab", B = "ba"
+ * Output: true
+ * Example 2:
+ *
+ * Input: A = "ab", B = "ab"
+ * Output: false
+ * Example 3:
+ *
+ * Input: A = "aa", B = "aa"
+ * Output: true
+ * Example 4:
+ *
+ * Input: A = "aaaaaaabc", B = "aaaaaaacb"
+ * Output: true
+ * Example 5:
+ *
+ * Input: A = "", B = "aa"
+ * Output: false
+ *
+ *
+ * Note:
+ *
+ * 0 <= A.length <= 20000
+ * 0 <= B.length <= 20000
+ * A and B consist only of lowercase letters.
+ */
+public class _859 {
+  public static class Solution1 {
+    public boolean buddyStrings(String A, String B) {
+      if (A.length() != B.length()) {
+        return false;
+      }
+      Character c1 = null;
+      Character c2 = null;
+      Set<Character> set = new HashSet<>();
+      int count = 0;
+      for (int i = 0; i < A.length(); i++) {
+        if (A.charAt(i) != B.charAt(i)) {
+          if (count > 2) {
+            return false;
+          }
+          if (c1 == null) {
+            c1 = B.charAt(i);
+            c2 = A.charAt(i);
+            count++;
+            continue;
+          }
+          if (c1 != A.charAt(i) || c2 != B.charAt(i)) {
+            return false;
+          }
+          count++;
+        }
+        set.add(A.charAt(i));
+      }
+      return count == 2 || (count == 0 && set.size() < A.length());
+    }
+  }
+}
diff --git a/src/test/java/com/fishercoder/_859Test.java b/src/test/java/com/fishercoder/_859Test.java
@@ -0,0 +1,46 @@
+package com.fishercoder;
+
+import com.fishercoder.solutions._859;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.TestCase.assertEquals;
+
+public class _859Test {
+  private static _859.Solution1 solution1;
+
+  @BeforeClass
+  public static void setup() {
+    solution1 = new _859.Solution1();
+  }
+
+  @Test
+  public void test1() {
+    assertEquals(true, solution1.buddyStrings("ab", "ba"));
+  }
+
+  @Test
+  public void test2() {
+    assertEquals(false, solution1.buddyStrings("ab", "ab"));
+  }
+
+  @Test
+  public void test3() {
+    assertEquals(true, solution1.buddyStrings("aa", "aa"));
+  }
+
+  @Test
+  public void test4() {
+    assertEquals(true, solution1.buddyStrings("aaaaaaabc", "aaaaaaacb"));
+  }
+
+  @Test
+  public void test5() {
+    assertEquals(false, solution1.buddyStrings("", "aa"));
+  }
+
+  @Test
+  public void test6() {
+    assertEquals(true, solution1.buddyStrings("aaa", "aaa"));
+  }
+}
