Array Rotation by Reversal in JavaScript

"use strict";
// Array Rotation by Reversal in JavaScript
//
// PURPOSE
// Three reversals rotate an array right without a second array.
//
// METHOD
// Normalize k modulo length. Reverse the whole array, then reverse the first k elements and
// the remaining suffix.
//
// COMPLEXITY
// O(n) time, O(1) auxiliary space.
//
// CONTRACT
// k >= 0. Rotates right in place, returns 0. Empty input is valid.
// 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: 0.
// Expected a after call: [4, 1, 2, 3].
// 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 rotate_right(a, k) {
    alg_require(a instanceof Int32Array);
    alg_require(Number.isInteger(k) && k >= -2147483648 && k <= 2147483647);
    let n = a.length;
    alg_require(((n >= 0) && (n <= 1000000)));
    alg_require((a.length == n));
    alg_require((k >= 0));
    if ((n == 0)) {
        return 0;
    }
    k = (k % n);
    let phase = 0;
    let left = 0;
    let right = 0;
    let temp = 0;
    while ((phase < 3)) {
        if ((phase == 0)) {
            left = 0;
            right = alg_sub(n, 1);
        } else {
            if ((phase == 1)) {
                left = 0;
                right = alg_sub(k, 1);
            } else {
                left = k;
                right = alg_sub(n, 1);
            }
        }
        while ((left < right)) {
            temp = a[left];
            a[left] = a[right];
            a[right] = temp;
            left = alg_add(left, 1);
            right = alg_sub(right, 1);
        }
        phase = alg_add(phase, 1);
    }
    return 0;
}

let a = new Int32Array([1, 2, 3, 4]);
let k = 1;
let result = rotate_right(a, k);
console.log(result);
// Expected a: [4, 1, 2, 3]
console.log(Array.from(a));