Next Lexicographic Permutation in JavaScript

"use strict";
// Next Lexicographic Permutation in JavaScript
//
// PURPOSE
// Next permutation advances a sequence to its immediate lexicographic successor, including
// sequences with duplicates.
//
// METHOD
// Find the rightmost ascent, swap its left element with the rightmost larger value, then
// reverse the descending suffix. If no ascent exists, reverse the entire array.
//
// COMPLEXITY
// O(n) time and O(1) auxiliary space.
//
// CONTRACT
// Mutates input. Returns 1 when advanced, 0 when wrapped to the first permutation.
// 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: 1.
// Expected a after call: [1, 3, 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 next_permutation(a) {
    alg_require(a instanceof Int32Array);
    let n = a.length;
    alg_require(((n >= 0) && (n <= 1000000)));
    alg_require((a.length == n));
    let pivot = alg_sub(n, 2);
    let right = alg_sub(n, 1);
    let left = 0;
    let temp = 0;
    let advanced = 0;
    while (((pivot >= 0) && (a[pivot] >= a[alg_add(pivot, 1)]))) {
        pivot = alg_sub(pivot, 1);
    }
    if ((pivot >= 0)) {
        while ((a[right] <= a[pivot])) {
            right = alg_sub(right, 1);
        }
        temp = a[pivot];
        a[pivot] = a[right];
        a[right] = temp;
        advanced = 1;
    }
    left = alg_add(pivot, 1);
    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);
    }
    return advanced;
}

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