Codility Demo Test Exercise Solution (JavaScript/NodeJS)

solution_codility_demo_test.js

// you can write to stdout for debugging purposes, e.g.
// console.log('this is a debug message');

function solution(A) {
    // write your code in JavaScript (Node.js 8.9.4)
    let tmp = []
    
    for (let i = 0; i < A.length; i++) {
        if (0 <= A[i]) {
            tmp[A[i]] = true
        }
    }
    
    for (let i = 1; i <= tmp.length; i++) {
        if (undefined === tmp[i]) {
            return i
        }
    }
    
    return 1
}

With 100% Score

function solution(A) {
    A = A.filter(x => x >= 1).sort((a, b) => a - b)

    let x = 1

    for(let i = 0; i < A.length; i++) {
        if(x < A[i]) {
            return x
        }
        x = A[i] + 1
    }

    return x
}