使用PHP在给定的数字数组中找到缺少的数字

Am new to php i have faced an interview some days ago, and the interviewer asked a question like the following one.

The given array has 99 numbers, which contains the digits from 1 to 100 with one digit missing. Describe two different algorithms that finds you the missing number. The algorithm should optimize for low storage and fast processing. Output should show the execution time of each algorithm.

And i have searched google about it, and come to know its a common puzzle used to ask in interviews. I found out the answer like this way.

int sum = 0;
int idx = -1;
for (int i = 0; i < arr.length; i++) {
    if (arr[i] == 0) {
         idx = i; 
    } else {
         sum += arr[i];
    }
}

// the total sum of numbers between 1 and arr.length.
int total = (arr.length + 1) * arr.length / 2;

System.out.println("missing number is: " + (total - sum) + " at index " + idx);

But the code is not in php,

Can u please help me to find out the php code and algorithm name. So i can improve my answer in the next interviews.

In PHP you can easily use some array functions and achieve that. Best way is,

$missing = array_diff(range(1,100),$array);

DEMO.

Another way to do it is by using the array_sum function and the knowledge that all numbers from 1 to 100 added together equals 5050.

$missing = 5050-array_sum($array);

Converted to PHP, it is nearly the same. (Not tested)

Of course, there are better ways, like the one Rikesh posted, but this is the exact one you asked for:

$sum = 0
$idx = -1
for($i = 0; $i < count($arr); $i++){
   if($arr[$i] == 0){
      $idx = $i;
   }else{
      $sum += $arr[$i];
   }
}

$total = (count($arr) + 1) * (count($arr) / 2);

echo "Missing: " . ($total - $sum) . " at index " . $idx;

$arr=range(1,99);
$j=1;
for($i=0;$i<100;$i++){
if(!in_array($j,$arr)){
    echo $j.'is missing';
}
$j++;
}