[LEET-530] add 530

Author: fishercoder1534

leetcode-algorithms/README.md

@@ -3,6 +3,7 @@
 ## Algorithms
 |  #  |      Title     |   Solutions   | Time          | Space         | Difficulty  | Tag          | Notes
 |-----|----------------|---------------|---------------|---------------|-------------|--------------|-----
+|530|[Minimum Absolute Difference in BST](https://leetcode.com/problems/minimum-absolute-difference-in-bst/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/MinimumAbsoluteDifferenceinBST.java) | O(n) |O(n) | Easy| DFS
 |520|[Detect Capital](https://leetcode.com/problems/detect-capital/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/DetectCapital.java) | O(n) |O(1) | Easy| 
 |515|[Find Largest Value in Each Tree Row](https://leetcode.com/problems/find-largest-value-in-each-tree-row/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FindLargestValueinEachTreeRow.java) | O(n) |O(k) | Medium| BFS
 |513|[Find Bottom Left Tree Value](https://leetcode.com/problems/find-bottom-left-tree-value/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FindBottomLeftValue.java) | O(n) |O(k) | Medium| BFS

leetcode-algorithms/src/main/java/com/stevesun/solutions/MinimumAbsoluteDifferenceinBST.java

@@ -0,0 +1,55 @@
+package com.stevesun.solutions;
+
+import com.stevesun.common.classes.TreeNode;
+
+import java.util.Iterator;
+import java.util.TreeSet;
+
+/**
+ * Given a binary search tree with non-negative values, find the minimum absolute difference between values of any two nodes.
+
+ Example:
+
+ Input:
+
+  1
+   \
+   3
+  /
+ 2
+
+ Output:
+ 1
+
+ Explanation:
+ The minimum absolute difference is 1, which is the difference between 2 and 1 (or between 2 and 3).
+ Note: There are at least two nodes in this BST.
+ */
+public class MinimumAbsoluteDifferenceinBST {
+
+    public int getMinimumDifference(TreeNode root) {
+        TreeSet<Integer> treeset = new TreeSet<>();
+        treeset.add(root.val);
+        dfs(root, treeset);
+        int diff = Integer.MAX_VALUE;
+        Iterator<Integer> iterator = treeset.iterator();
+        int prev = iterator.next();
+        while (iterator.hasNext()) {
+            int current = iterator.next();
+            diff = Math.min(diff, Math.abs(current - prev));
+            prev = current;
+        }
+        return diff;
+    }
+
+    private void dfs(TreeNode root, TreeSet<Integer> treeset) {
+        if (root.left != null) {
+            treeset.add(root.left.val);
+            dfs(root.left, treeset);
+        }
+        if (root.right != null) {
+            treeset.add(root.right.val);
+            dfs(root.right, treeset);
+        }
+    }
+}

leetcode-algorithms/src/test/java/com/stevesun/MinimumAbsoluteDifferenceinBSTTest.java

@@ -0,0 +1,60 @@
+package com.stevesun;
+
+import com.stevesun.common.classes.TreeNode;
+import com.stevesun.solutions.MinimumAbsoluteDifferenceinBST;
+import org.junit.Before;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static junit.framework.Assert.assertEquals;
+
+public class MinimumAbsoluteDifferenceinBSTTest {
+    private static MinimumAbsoluteDifferenceinBST test;
+    private static int expected;
+    private static int actual;
+    private static TreeNode root;
+
+    @BeforeClass
+    public static void setup(){
+        test = new MinimumAbsoluteDifferenceinBST();
+    }
+
+    @Before
+    public void setupForEachTest(){
+        expected = 0;
+        actual = 0;
+    }
+
+    @Test
+    public void test1(){
+        root = new TreeNode(1);
+        root.right = new TreeNode(3);
+        root.right.left = new TreeNode(2);
+        expected = 1;
+        actual = test.getMinimumDifference(root);
+        assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test2(){
+        root = new TreeNode(1);
+        root.right = new TreeNode(5);
+        root.right.left = new TreeNode(3);
+        expected = 2;
+        actual = test.getMinimumDifference(root);
+        assertEquals(expected, actual);
+    }
+
+//    [543,384,652,null,445,null,699]
+    @Test
+    public void test3() {
+        root = new TreeNode(543);
+        root.left = new TreeNode(384);
+        root.right = new TreeNode(652);
+        root.left.right = new TreeNode(445);
+        root.right.right = new TreeNode(699);
+        expected = 47;
+        actual = test.getMinimumDifference(root);
+        assertEquals(expected, actual);
+    }
+}