add 594

Author: fishercoder1534

README.md

@@ -20,6 +20,7 @@ Your ideas/fixes/algorithms are more than welcome!
 
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
+|594|[Longest Harmonious Subsequence](https://leetcode.com/problems/longest-harmonious-subsequence/)|[Solution](../master/src/main/java/com/stevesun/solutions/_594.java) | O(n) |O(n) | Easy | Array, HashMap
 |583|[Delete Operation for Two Strings](https://leetcode.com/problems/delete-operation-for-two-strings/)|[Solution](../master/src/main/java/com/stevesun/solutions/_583.java) | O(m*n) |O(m*n) could be optimized to O(n) | Medium | DP
 |582|[Kill Process](https://leetcode.com/problems/kill-process/)|[Solution](../master/src/main/java/com/stevesun/solutions/_582.java) | O(n) |O(h) | Medium | Stack
 |581|[Shortest Unsorted Continuous Subarray](https://leetcode.com/problems/shortest-unsorted-continuous-subarray/)|[Solution](../master/src/main/java/com/stevesun/solutions/_581.java) | O(n) |O(1) | Easy | Array, Sort

src/main/java/com/stevesun/solutions/_594.java

@@ -0,0 +1,35 @@
+package com.stevesun.solutions;
+
+import java.util.*;
+
+/**
+ * 594. Longest Harmonious Subsequence
+ *
+ * We define a harmonious array is an array where the difference between its maximum value and its minimum value is exactly 1.
+
+ Now, given an integer array, you need to find the length of its longest harmonious subsequence among all its possible subsequences.
+
+ Example 1:
+ Input: [1,3,2,2,5,2,3,7]
+ Output: 5
+
+ Explanation: The longest harmonious subsequence is [3,2,2,2,3].
+ Note: The length of the input array will not exceed 20,000.
+
+ */
+public class _594 {
+    public int findLHS(int[] nums) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int i : nums) {
+            map.put(i, map.getOrDefault(i, 0) + 1);
+        }
+        int max = 0;
+        for (int i = 0; i < nums.length; i++) {
+            if (map.containsKey(nums[i]+1)) {
+                max = Math.max(max, map.get(nums[i]) + map.get(nums[i] + 1));
+            }
+        }
+        return max;
+    }
+
+}

src/test/java/com/stevesun/_594Test.java

@@ -0,0 +1,27 @@
+package com.stevesun;
+
+import com.stevesun.solutions._48;
+import com.stevesun.solutions._594;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Created by stevesun on 5/20/17.
+ */
+public class _594Test {
+    private static _594 test;
+    private static int[] nums;
+
+    @BeforeClass
+    public static void setup(){
+        test = new _594();
+    }
+
+    @Test
+    public void test1(){
+        nums = new int[]{1,3,2,2,5,2,3,7};
+        assertEquals(5, test.findLHS(nums));
+    }
+}