Binary Search Tree Lookup in JavaScript

"use strict";
// Binary Search Tree Lookup in JavaScript
//
// PURPOSE
// A binary search tree chooses a branch by comparing the target with the current node key.
//
// METHOD
// At each node return on equality, otherwise follow the left child for a smaller target or
// the right child for a larger target.
//
// COMPLEXITY
// O(height) time and O(1) auxiliary space; height is O(log n) only when the tree is
// balanced.
//
// CONTRACT
// keys,left_child,right_child have n entries; -1 means absent. Must be a valid BST. Returns
// node ID or -1.
// Public APIs infer array lengths except in C, which accepts pointer/length pairs. Vertex
// counts and matrix dimensions remain explicit. Arrays must contain signed 32-bit integers.
// Sorted order, correct tree topology, and caller-owned data-structure invariants are
// preconditions; checking them on every query would change query complexity.
// Scalar and shape checks are included. Value-range checks are included where needed to
// prevent invalid indexing or nontermination. Allocation sizes are capped at 4,000,000
// workspace entries. Arithmetic outside Python raises an error on 32-bit overflow; Python
// uses arbitrary precision. Native allocation failures propagate. In-place outputs may be
// partly updated after arithmetic failure. These are single-threaded, in-memory
// implementations.
//
// LANGUAGE DETAILS
// Node.js 18+: Int32Array inputs and workspaces provide compact integer storage. Automatic
// lengths and checked arithmetic reject values outside signed 32-bit. Invalid inputs or
// overflow throw RangeError.
//
// EXAMPLE
// Expected return: 2.
// Run: node example.js
// Tests for this exact source artifact run before publication. The accompanying source
// archive includes unit cases, runtime results, and source hashes.

function alg_require(valid) { if (!valid) throw new RangeError("invalid algorithm input"); }
function alg_checked(v) { if (!Number.isInteger(v) || v < -2147483648 || v > 2147483647) throw new RangeError("32-bit result overflow"); return v; }
function alg_add(a,b) { return alg_checked(a+b); }
function alg_sub(a,b) { return alg_checked(a-b); }
function alg_mul(a,b) { return alg_checked(a*b); }
function alg_size(n) { alg_require(Number.isInteger(n) && n>=0 && n<=4000000); return n; }

function bst_lookup(keys, left_child, right_child, root, target) {
    alg_require(keys instanceof Int32Array);
    alg_require(left_child instanceof Int32Array);
    alg_require(right_child instanceof Int32Array);
    alg_require(Number.isInteger(root) && root >= -2147483648 && root <= 2147483647);
    alg_require(Number.isInteger(target) && target >= -2147483648 && target <= 2147483647);
    let n = keys.length;
    alg_require(((n >= 0) && (n <= 1000000)));
    alg_require((keys.length == n));
    alg_require((left_child.length == n));
    alg_require((right_child.length == n));
    alg_require(((root >= alg_sub(0, 1)) && (root < n)));
    for (let alg_i = 0; alg_i < left_child.length; alg_i++) {
        let alg_value = left_child[alg_i];
        alg_require(((alg_value >= alg_sub(0, 1)) && (alg_value < n)));
    }
    for (let alg_i = 0; alg_i < right_child.length; alg_i++) {
        let alg_value = right_child[alg_i];
        alg_require(((alg_value >= alg_sub(0, 1)) && (alg_value < n)));
    }
    while ((root != alg_sub(0, 1))) {
        if ((keys[root] == target)) {
            return root;
        }
        if ((target < keys[root])) {
            root = left_child[root];
        } else {
            root = right_child[root];
        }
    }
    return alg_sub(0, 1);
}

let keys = new Int32Array([4, 2, 6]);
let left_child = new Int32Array([1, -1, -1]);
let right_child = new Int32Array([2, -1, -1]);
let root = 0;
let target = 6;
let result = bst_lookup(keys, left_child, right_child, root, target);
console.log(result);