Find Closest Value in BTS

Find Closest Value in BTS

Write a function that takes in a Binary Search Tree (BST) and a target integer value and returns the closest value to that target value contained in the BST.

You can assume that there will only be one closest value.

Each BST node has an integer value, a left child node, and a right child node. A node is said to be a valid BST node if and only if it satisfies the BST property: its value is strictly greater than the values of every node to its left; its value is less than or equal to the values of every node to its right; and its children nodes are either valid BST nodes themselves or None / null.

Sample Input

tree =   10
       /     \
      5      15
    /   \   /   \
   2     5 13   22
 /           \
1            14
target = 12

Sample Output

13

Solution 1

// O(log(n)) time | O(log(n)) space
function findClosestValueInBst(tree, target) {
  return findClosestValueInBstHelper(tree, target, tree.value);
}

function findClosestValueInBstHelper(tree, target, closest) {
  if (tree === null) return closest;
  if (Math.abs(target - closest) > Math.abs(target - tree.value)) {
    closest = tree.value;
  }
  if (target < tree.value) {
    return findClosestValueInBstHelper(tree.left, target, closest);
  } else if (target > tree.value) {
    return findClosestValueInBstHelper(tree.right, target, closest);
  } else {
    return closest; 
  }
}

// This is the class of the input tree. Do not edit.
class BST {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

// Do not edit the line below.
exports.findClosestValueInBst = findClosestValueInBst;

Solution 2

// O(log(n)) time | O(1) space
function findClosestValueInBst(tree, target) {
  return findClosestValueInBstHelper(tree, target, tree.value);
}

function findClosestValueInBstHelper(tree, target, closest) {
  let currentNode = tree;
  while (currentNode !== null) {
    if (Math.abs(target - closest) > Math.abs(target - currentNode.value)) {
      closest = currentNode.value; 
    }
    if (target < currentNode.value) {
      currentNode = currentNode.left;
    } else if (target > currentNode.value) {
      currentNode = currentNode.right
    } else {
      break;
    }
  }
  return closest
}

// This is the class of the input tree. Do not edit.
class BST {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

// Do not edit the line below.
exports.findClosestValueInBst = findClosestValueInBst;