php - 这个解决方案有什么问题？ (Perm-Missing-Elem codility test)

Question

我已经开始玩 codility 并遇到了这个问题:

A zero-indexed array A consisting of N different integers is given. The array contains integers in the range [1..(N + 1)], which means that exactly one element is missing.

Your goal is to find that missing element.

Write a function:

int solution(int A[], int N); 

that, given a zero-indexed array A, returns the value of the missing element.

For example, given array A such that:

A[0] = 2 A[1] = 3 A[2] = 1 A[3] = 5

the function should return 4, as it is the missing element.

Assume that:

    N is an integer within the range [0..100,000];
    the elements of A are all distinct;
    each element of array A is an integer within the range [1..(N + 1)].

Complexity:

    expected worst-case time complexity is O(N);
    expected worst-case space complexity is O(1), beyond input storage (not counting the storage required for input arguments).

我已经提交了以下解决方案(用 PHP):

function solution($A) {
    $nr = count($A);
    $totalSum = (($nr+1)*($nr+2))/2;
    $arrSum = array_sum($A);
    return ($totalSum-$arrSum);
}

它给了我 66 分(满分 100 分)，因为它没有通过涉及大型数组的测试:“large_range 范围序列，长度 = ~100,000”结果:运行时错误测试程序意外终止标准输出:无效的结果类型，预期为 int。

我在本地测试了一个包含 100.000 个元素的数组，它没有任何问题。那么，我的代码似乎有什么问题，codility 使用了什么样的测试用例来返回“无效的结果类型，int expected”？

Answer 1

PermMissingElem 的 100/100 php 解决方案:

function solution($A) {   
    $N   = count($A);
    $sum = ($N + 2) * ($N + 1) / 2;
    for($i = 0; $i < $N; $i++){
        $sum -= $A[$i];
    }
    return intval($sum);
}