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700. Search in a Binary Search Tree

Problem Description

Given the root node of a binary search tree (BST) and a value. You need to find the node in the BST that the node's value equals the given value. Return the subtree rooted with that node. If such node doesn't exist, you should return NULL.

Detail instruction can be found here.

Example 1:

Given the tree:
        4
       / \
      2   7
     / \
    1   3

And the value to search: 2

Output:
      2     
     / \   
    1   3

Solution

Approach 1: Recursive

public TreeNode searchBST(TreeNode root, int val) {
      if (root == null)
          return null;
      
      if      (val < root.val)    return searchBST(root.left, val);
      else if (val > root.val)    return searchBST(root.right, val);
      else                        return root;
  }

Approach 2: Iterative

public TreeNode searchBST(TreeNode root, int val) {
      TreeNode x = root;
      while (x != null) {
          if      (x.val == val)  return x;
          else if (val > x.val)   x = x.right;
          else                    x = x.left;
      }
      return x;
  }

Definition for a binary tree node.

public class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int x) { val = x; }
}

Test

Compile with javac Solution.java and run with java Solution.

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