Array Rotation by Reversal in Python

from bisect import bisect_left

# Array Rotation by Reversal in Python
#
# 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
# Python 3.9+: automatic lengths, native lists, arbitrary-precision arithmetic, and
# bisect_left for LIS. Invalid scalar/shape inputs raise ValueError. Integer element types
# and sorted/tree invariants remain caller preconditions.
#
# EXAMPLE
# Expected return: 0.
# Expected a after call: [4, 1, 2, 3].
# Run: python example.py
# Tests for this exact source artifact run before publication. The accompanying source
# archive includes unit cases, runtime results, and source hashes.

def alg_require(condition):
    if not condition:
        raise ValueError("invalid algorithm input; see contract")
def alg_size(n):
    alg_require(0 <= n <= 4000000)
    return n

def rotate_right(a: list[int], k: int) -> int:
    alg_require(isinstance(a, list) and len(a) <= 1000000)
    alg_require(type(k) is int and -2147483648 <= k <= 2147483647)
    n: int = len(a)
    alg_require(n >= 0 and n <= 1000000)
    alg_require(len(a) == n)
    alg_require(k >= 0)
    if n == 0:
        return 0
    k = k % n
    phase: int = 0
    left: int = 0
    right: int = 0
    temp: int = 0
    while phase < 3:
        if phase == 0:
            left = 0
            right = n - 1
        elif phase == 1:
            left = 0
            right = k - 1
        else:
            left = k
            right = n - 1
        while left < right:
            temp = a[left]
            a[left] = a[right]
            a[right] = temp
            left += 1
            right -= 1
        phase += 1
    return 0

a = [1, 2, 3, 4]
k = 1
result = rotate_right(a, k)
print(result)
# Expected a: [4, 1, 2, 3]
print(a)