试图在 JavaScript 的 BST 中找到最接近的值

Question

Trying to follow along with this write up on Find the Closest Value in a Binary Search Tree . However, I am getting undefined returned instead of 13. Below is the code that also includes the tree data. The write up has an alternate more optimized solution but I'm just trying to first understand the less optimized version first. I'm missing a step but can't find it. What am I missing. Thank you.

[

 const treeData = { "target": 12, "tree": { "nodes": [ {"id": "10", "left": "5", "right": "15", "value": 10}, {"id": "15", "left": "13", "right": "22", "value": 15}, {"id": "22", "left": null, "right": null, "value": 22}, {"id": "13", "left": null, "right": "14", "value": 13}, {"id": "14", "left": null, "right": null, "value": 14}, {"id": "5", "left": "2", "right": "5-2", "value": 5}, {"id": "5-2", "left": null, "right": null, "value": 5}, {"id": "2", "left": "1", "right": null, "value": 2}, {"id": "1", "left": null, "right": null, "value": 1} ], "root": "10" } }; class BST { constructor(value) { this.value = value; this.left = null; this.right = null; } }; const findClosestValueInBst = (tree, target) => { // define current node as input tree let currentNode = tree; //console.log(tree); // create array to store BST values const values = []; // traverse the tree and place all values in the above array const traverse = node => { if (node) { traverse(node.left); values.push(node.value); traverse(node.right); } } traverse(tree); // create closestProximity variable let closestProximity = Number.POSITIVE_INFINITY; //console.log(closestProximity); // create undefined closestValue variable let closestValue; // iterate over the values array, checking each value's proximity to the target value for (let i = 0; i < values.length; i++) { let proximity = Math.abs(values[i] - target); // if closer in proximity than closestProximity, replace closestProximity if (proximity < closestProximity) { // update closestValue closestValue = values[i]; } } return closestValue; }; const result = findClosestValueInBst(treeData.tree, treeData.target); console.log(result);

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Answer 1

After the corrections made in your question, there are still these issues:

• The code never updates closestProximity so the if condition on this variable will always be true.
• The main call passes treeData.tree to the function, but that function then treats that reference as a node object, never looking into the nodes property.
• The input data is not transformed into instances of BST , which means that you cannot navigate efficiently through the tree. Even if you would have a node object, then node.left is just a string, not an object, and you'd have to scan the tree.nodes array to locate the corresponding object.
• By first collecting the nodes into an array through traverse you lose any benefit from the binary search tree. The purpose of this data structure is to avoid having to visit all values.

Here is a correction of your code that addresses these issues:

 class BST { constructor(value) { this.value = value; this.left = null; this.right = null; } } function loadTree(tree) { const nodeMap = new Map(tree.nodes.map(node => [node.id, new BST(node.value)])); for (const node of tree.nodes) { nodeMap.get(node.id).left = nodeMap.get(node.left)?? null; nodeMap.get(node.id).right = nodeMap.get(node.right)?? null; } return nodeMap.get(tree.root); } function findClosestValueInBst(root, target) { let currentNode = root; let high = Infinity; let low = -Infinity; while (currentNode) { if (target < currentNode.value) { high = currentNode.value; currentNode = currentNode.left; } else { low = currentNode.value; currentNode = currentNode.right; } } return high - target < target - low? high: low; } const treeData = {"target": 12,"tree": {"nodes": [{"id": "10", "left": "5", "right": "15", "value": 10},{"id": "15", "left": "13", "right": "22", "value": 15},{"id": "22", "left": null, "right": null, "value": 22},{"id": "13", "left": null, "right": "14", "value": 13},{"id": "14", "left": null, "right": null, "value": 14},{"id": "5", "left": "2", "right": "5-2", "value": 5},{"id": "5-2", "left": null, "right": null, "value": 5},{"id": "2", "left": "1", "right": null, "value": 2},{"id": "1", "left": null, "right": null, "value": 1}],"root": "10"}}; const result = findClosestValueInBst(loadTree(treeData.tree), treeData.target); console.log(result);