Alpha 2010.php

<?php

/*
A non-empty zero-indexed array A consisting of N integers is given. The first covering prefix of array A is 
the smallest integer P such that 0 ≤ P < N and such that every value that occurs in array A also occurs in sequence 
A[0], A[1], ..., A[P].

For example, the first covering prefix of the following 5−element array A:
A[0] = 2
A[1] = 2
A[2] = 1
A[3] = 0
A[4] = 1

is 3, because sequence [ A[0], A[1], A[2], A[3] ] equal to [2, 2, 1, 0], contains all values that occur in array A.

Write a function

    function solution($A);

that, given a zero-indexed non-empty array A consisting of N integers, returns the first covering prefix of A.

For example, given array A such that
A[0] = 2
A[1] = 2
A[2] = 1
A[3] = 0
A[4] = 1

the function should return 3, as explained above.

Assume that:
        N is an integer within the range [1..1,000,000];
        each element of array A is an integer within the range [0..N−1].

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.
*/

/*
 * CODILITY ANALYSIS: https://codility.com/demo/results/trainingFYCGTU-5BG/
 * LEVEL: EASY
 * Correctness:	100%
 * Performance:	100%
 * Task score:	100%
 */
function solution($A)
{
	// array which contains only the first integer occurences: array($integer => $position, ...)
	$firstUniques = array();
	foreach($A as $index => $integer)
	{
		// If first occurence was not found until now
		if(!isset($firstUniques[$integer]))
			$firstUniques[$integer] = $index;
	}

	// Unique element which was last added represents the first covering prefix of array $A
	$lastUniqueElementPosition = end($firstUniques);

	return $lastUniqueElementPosition;
}