Finding missing number in an array

Question

I want to have a function that would browse through the natural numbers array of any size ({0,1,2....}) and find a missing value.

What i mean is that if the array is e.g : {0,1,3,4,5} i want the function to return 2, if array is {1,3,0,4} i want the function to return 2 and so on...

My attempt is:

int missing(int* t, int r) {
    int i;
    int sum=0;
    sum=(r+1)*(r+2)/2;
    for(i=0;t[i];i++){
        sum-=t[i];
    }
    return sum;
}

The idea was to first calculate the sum from 1 to n and than subtract from this sum each number in an array separately. However the program returns total sum without subtraction of the numbers in an array.

Why it is not working correctly?

for(i=0;t[i];i++) this makes no sense at all - did you mean for(i = 0; i < r; i++)? — Random Davis
– Random Davis, Commented Nov 7, 2016 at 19:23

Alex Aparin · Accepted Answer · 2016-11-07 19:40:31Z

2

Use condition i < r instead t[i]. First value of sequence is zero, therefore loop is not traversed

Moreover you can use optimized version of algorithm (unfortunately I don't have opportunity to test code -- it is just idea for only sorted array)

int res = 0;
for (int i = 0; i < r && t[i] == res; ++i, ++res) ;

edited Nov 7, 2016 at 19:40

answered Nov 7, 2016 at 19:20

Alex Aparin

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Comments

wafL · Accepted Answer · 2022-12-13 18:46:35Z

-1

This function allows you to find missing numbers within the given array.

<?PHP

function FindMissingArr($args)
{
    $max = max($args);
    $min = min($args);


    $range = range($min, $max);

    $find = [];

    $result = array_diff($range, $args);

    foreach ($result as $key => $value) {
        array_push($find, $value);
    }

    return $find;
}~

$arr = array(1, 5, 8, 21);
print_r(FindMissingArr($arr));

?>

Result:

Array ( [0] => 2 [1] => 3 [2] => 4 [3] => 6 [4] => 7 [5] => 9 [6] => 10 [7] => 11 [8] => 12 [9] => 13 [10] => 14 [11] => 15 [12] => 16 [13] => 17 [14] => 18 [15] => 19 [16] => 20 )

edited Dec 13, 2022 at 18:46

wafL

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answered Dec 9, 2022 at 10:38

M. Surguli

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