Monotonic Deque Sliding Maximum in JavaScript

"use strict";
// Monotonic Deque Sliding Maximum in JavaScript
//
// PURPOSE
// A monotonic deque returns every fixed-window maximum in linear time.
//
// METHOD
// Keep candidate indices in decreasing value order. Discard expired indices from the front
// and dominated candidates from the back; the front is the current maximum.
//
// COMPLEXITY
// O(n) time; O(n) allocated index-buffer space in this linear-buffer implementation, with at
// most k live candidates.
//
// CONTRACT
// 1 <= k <= n. output has n-k+1 entries. Writes maximum values and returns output length.
// 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: 6.
// Expected output after call: [3, 3, 5, 5, 6, 7].
// 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 sliding_maximum(a, k, output) {
    alg_require(a instanceof Int32Array);
    alg_require(Number.isInteger(k) && k >= -2147483648 && k <= 2147483647);
    alg_require(output instanceof Int32Array);
    let n = a.length;
    alg_require(((n >= 0) && (n <= 1000000)));
    alg_require((a.length == n));
    alg_require((output.length == alg_add(alg_sub(n, k), 1)));
    alg_require(((k >= 1) && (k <= n)));
    let queue = new Int32Array(alg_size(n));
    let head = 0;
    let tail = 0;
    let i = 0;
    while ((i < n)) {
        while (((head < tail) && (queue[head] <= alg_sub(i, k)))) {
            head = alg_add(head, 1);
        }
        while (((head < tail) && (a[queue[alg_sub(tail, 1)]] <= a[i]))) {
            tail = alg_sub(tail, 1);
        }
        queue[tail] = i;
        tail = alg_add(tail, 1);
        if ((i >= alg_sub(k, 1))) {
            output[alg_add(alg_sub(i, k), 1)] = a[queue[head]];
        }
        i = alg_add(i, 1);
    }
    return alg_add(alg_sub(n, k), 1);
}

let a = new Int32Array([1, 3, -1, -3, 5, 3, 6, 7]);
let k = 3;
let output = new Int32Array([0, 0, 0, 0, 0, 0]);
let result = sliding_maximum(a, k, output);
console.log(result);
// Expected output: [3, 3, 5, 5, 6, 7]
console.log(Array.from(output));