Add solution of RangeSumOfBST task

Author: andrei-punko

src/main/java/by/andd3dfx/tree/RangeSumOfBST.java

@@ -0,0 +1,63 @@
+package by.andd3dfx.tree;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * <pre>
+ * <a href="https://leetcode.com/problems/range-sum-of-bst/description/">Task description</a>
+ *
+ * Given the root node of a binary search tree and two integers low and high, return the sum of values of all nodes with a value
+ * in the inclusive range [low, high].
+ *
+ * Example 1:
+ * <img src="https://assets.leetcode.com/uploads/2020/11/05/bst1.jpg"/>
+ *   Input: root = [10,5,15,3,7,null,18], low = 7, high = 15
+ *   Output: 32
+ *   Explanation: Nodes 7, 10, and 15 are in the range [7, 15]. 7 + 10 + 15 = 32.
+ *
+ * Example 2:
+ * <img src="https://assets.leetcode.com/uploads/2020/11/05/bst2.jpg"/>
+ *   Input: root = [10,5,15,3,7,13,18,1,null,6], low = 6, high = 10
+ *   Output: 23
+ *   Explanation: Nodes 6, 7, and 10 are in the range [6, 10]. 6 + 7 + 10 = 23.
+ * </pre>
+ */
+public class RangeSumOfBST {
+
+    public static int rangeSumBST(TreeNode root, int low, int high) {
+        Deque<TreeNode> queue = new ArrayDeque<>();
+        queue.add(root);
+        var sum = 0;
+        while (!queue.isEmpty()) {
+            var element = queue.pop();
+            if (element.left != null) {
+                queue.add(element.left);
+            }
+            if (element.right != null) {
+                queue.add(element.right);
+            }
+            if (low <= element.val && element.val <= high) {
+                sum += element.val;
+            }
+        }
+        return sum;
+    }
+
+    public static class TreeNode {
+
+        int val;
+        TreeNode left;
+        TreeNode right;
+
+        TreeNode(int val) {
+            this.val = val;
+        }
+
+        TreeNode(int val, TreeNode left, TreeNode right) {
+            this.val = val;
+            this.left = left;
+            this.right = right;
+        }
+    }
+}

src/test/java/by/andd3dfx/tree/RangeSumOfBSTTest.java

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+package by.andd3dfx.tree;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import by.andd3dfx.tree.RangeSumOfBST.TreeNode;
+import org.junit.Test;
+
+public class RangeSumOfBSTTest {
+
+    @Test
+    public void rangeSumBST() {
+        TreeNode root = new TreeNode(10,
+            new TreeNode(5, new TreeNode(3), new TreeNode(7)),
+            new TreeNode(15, null, new TreeNode(18))
+        );
+        assertThat(RangeSumOfBST.rangeSumBST(root, 7, 15)).isEqualTo(32);
+
+        TreeNode root2 = new TreeNode(10,
+            new TreeNode(5,
+                new TreeNode(3, new TreeNode(1), null),
+                new TreeNode(7, new TreeNode(6), null)
+            ),
+            new TreeNode(15, new TreeNode(13), new TreeNode(18))
+        );
+        assertThat(RangeSumOfBST.rangeSumBST(root2, 6, 10)).isEqualTo(23);
+    }
+}