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<N;i++){
        sum=sum + (long long)A[i];
    }

    if (N%2==0){
        Nsum= (N+1)*((N+2)/2);
        return (int)(Nsum-sum);
    }
    else{
        Nsum= ((N+1)/2)*(N+2);
        return (int)(Nsum-sum);
    }    

}

This gave the 100/100 score.

Answer 2

100%: the Python sort routine is not regarded as cheating...

def solution(A):
    """
    Sort the array then loop till the value is higher than expected
    """
    missing = 1
    for elem in sorted(A):
        if elem == missing:
            missing += 1
        if elem > missing:
            break
    return missing

Answer 3

My 100/100 solution

  public int solution(int[] A) {
        Arrays.sort(A);
        for (int i = 1; i < 1_000_000; i++) {
            if (Arrays.binarySearch(A, i) < 0){
                return i;
            }
        }
        return -1;
    }

Answer 4

JavaScript 100%

function solution(A) {
  let sortedOb = {};
  let biggest = 0;

  A.forEach(el => {
    if (el > 0) {
      sortedOb[el] = 0;
      biggest = el > biggest ? el : biggest;
    }
  });
  let arr = Object.keys(sortedOb).map(el => +el);
  if (arr.length == 0) return 1;

  for(let i = 1; i <= biggest; i++) {
    if (sortedOb[i] === undefined) return i;
  }
  return biggest + 1;
}

Answer 5

This is my solution is Swift 4

public func solution(_ A: inout [Int]) -> Int {

    var minNum = 1
    var hashSet = Set<Int>()

    for int in A {
        if int > 0 {
            hashSet.insert(int)
        }
    }

    while hashSet.contains(minNum) {
        minNum += 1
    }

    return minNum

}

var array = [1,3,6]

solution(&array)

// Answer: 2

Answer 6

This is my solution using python:

def solution(A):
    m = max(A)

    if m <= 0:
        return 1

    if m == 1:
        return 2

    # Build a sorted list with all elements in A
    s = sorted(list(set(A)))

    b = 0

    # Iterate over the unique list trying to find integers not existing in A
    for i in xrange(len(s)):
        x = s[i]

        # If the current element is lte 0, just skip it
        if x <= 0:
            continue;

        b = b + 1

        # If the current element is not equal to the current position,
        # it means that the current position is missing from A
        if x != b:
            return b

    return m + 1

Scored 100%/100% https://codility.com/demo/results/demoDCU7CA-SBR/