PermCheck

* PermCheck * 

A non-empty 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 an 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.

Write an efficient algorithm for the following assumptions:

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].

**************************************** SOLUTION ************************************************
function solution($A) {
 
    if (empty($A)) {
        return 0;
    }

    sort($A);

    $length = count($A);

    if ($length < 1 || $length > 100000) {
        return 0;
    }

    $j         = 1;
    $tmpNumber = 0;

    for ($i = 0; $i < $length; $i++, $j++) {

        if (!is_integer($A[$i]) || ($A[$i] < 1 || $A[$i] > 1000000000)) {
            return 0;
        }

        if (($j !== $A[$i]) || ($tmpNumber == $A[$i])) {
            return 0;
        }

        $tmpNumber = $A[$i];
    }

    return 1;
}