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by sweetcoco

HTML

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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:
function 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.

-->

JavaScript

function solution(A) {
    A.sort(function(a, b){return b-a});
    
    if (A.length < 2) { return 0; }
    
    if (Math.abs(A[0] - A[(A.length - 1)]) + 1 !== A.length) {
       return 0;
    }

   for (i = 0; i < A.length - 1; i++) {
           if (A[i] === A[(i+1)]) { return 0;}
       }
       
       return 1;
       
   
}