Validate Binary Search Tree - Recursive

Author: dksifoua

src/main/java/io/dksifoua/leetcode/validatebinarysearchtree/Solution.java

@@ -27,4 +27,17 @@ public boolean isValidBST(TreeNode root) {
 
         return true;
     }
+
+    public boolean isValidBSTRecursive(TreeNode root) {
+        return dfs(root, Long.MIN_VALUE, Long.MAX_VALUE);
+    }
+
+    private boolean dfs(TreeNode node, long minValue, long maxValue) {
+        if (node == null) return true;
+
+        if (node.getValue() <= minValue || node.getValue() >= maxValue) return false;
+
+        return dfs(node.getLeft(), minValue, (long) node.getValue())
+                && dfs(node.getRight(), (long) node.getValue(), maxValue);
+    }
 }

src/test/java/io/dksifoua/leetcode/validatebinarysearchtree/SolutionTest.java

@@ -15,18 +15,38 @@ void test1() {
         assertTrue(solution.isValidBST(TreeNode.build(new Integer[] { 2, 1, 3 })));
     }
 
+    @Test
+    void test1Recursive() {
+        assertTrue(solution.isValidBSTRecursive(TreeNode.build(new Integer[] { 2, 1, 3 })));
+    }
+
     @Test
     void test2() {
         assertFalse(solution.isValidBST(TreeNode.build(new Integer[] { 5, 1, 4, null, null, 3, 6 })));
     }
 
+    @Test
+    void test2Recursive() {
+        assertFalse(solution.isValidBSTRecursive(TreeNode.build(new Integer[] { 5, 1, 4, null, null, 3, 6 })));
+    }
+
     @Test
     void test3() {
         assertTrue(solution.isValidBST(TreeNode.build(new Integer[] { 2147483647 })));
     }
 
+    @Test
+    void test3Recursive() {
+        assertTrue(solution.isValidBSTRecursive(TreeNode.build(new Integer[] { 2147483647 })));
+    }
+
     @Test
     void test4() {
         assertFalse(solution.isValidBST(TreeNode.build(new Integer[] { 2, 2, 2 })));
     }
+
+    @Test
+    void test4Recursive() {
+        assertFalse(solution.isValidBSTRecursive(TreeNode.build(new Integer[] { 2, 2, 2 })));
+    }
 }