"""

PermCheck
Check whether array A is a permutation.
https://codility.com/demo/results/demoANZ7M2-GFU/

Task description
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(A):
    # write your code in Python 2.7
    s = set(A)
    N_set = len(s) #O(n)
    N = len(A)
    if N != N_set: return 0
    
    sum_N = N*(N+1)/2  #O(1)
    sum_A = sum(A)  #O(n)
    return 1 if sum_N == sum_A else 0
[]