Perm-Missing-Elem

Perm-Missing-Elem.js

/*
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)].

*/

function solution(A) {
    // write your code in JavaScript (ECMA-262, 5th edition)
    result = 0;
    if (!A || A.length == 0) return result;
    np1 = A.length + 1;
    sum = np1 * (1 + np1) / 2;
    sumOfA = A.reduce(function(prev, current) {
        return prev + current;
    });
    result = sum - sumOfA;
    return result;
}

just a small correction .... the answer for no array or array.length === 0 is 1 because the problem defines a range of [1..(N + 1)] ..trick....