check_permutation.py

"""
A non-empty zero-indexed array A consisting of N integers is given.

A permutation is a sequence containing each element from 1 to N once, and only once.

For example, array A such that:

    A[0] = 4
    A[1] = 1
    A[2] = 3
    A[3] = 2
is a permutation, but array A such that:

    A[0] = 4
    A[1] = 1
    A[2] = 3
is not a permutation, because value 2 is missing.

The goal is to check whether array A is a permutation.

Write a function:

def solution(A)

that, given a zero-indexed array A, returns 1 if array A is a permutation
and 0 if it is not.

For example, given array A such that:

    A[0] = 4
    A[1] = 1
    A[2] = 3
    A[3] = 2
the function should return 1.

Given array A such that:

    A[0] = 4
    A[1] = 1
    A[2] = 3
the function should return 0.

Assume that:

N is an integer within the range [1..100,000];
each element of array A is an integer within the range [1..1,000,000,000].
Complexity:

expected worst-case time complexity is O(N);
expected worst-case space complexity is O(N), beyond input storage
 (not counting the storage required for input arguments).
Elements of input arrays can be modified.
"""


def solution(nums):
    """Check if given nums are permutation 1..N."""
    if not nums:
        return 0
    seen = set()
    for num in nums:
        if num < 1 or num > len(nums) or num in seen:
            return 0
        seen.add(num)
    return 1