Missing integer variation - O(n) solution needed [closed]

Answer 1

Code for C, in fact, this can be used for any programming language without any change in the logic.

Logic is sum of N number is N*(N+1)/2.

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

    // write your code in C99
    long long sum=0;
    long long i;
    long long Nsum=0;

    for(i=0;i

This gave the 100/100 score.