Solution to Missing-Integer by codility | Code Says


Solution to Missing-Integer by codility | Code Says
Question: https://codility.com/demo/take-sample-test/missing_integer
Write a function:
int solution(int A[], int N);
that, given a non-empty zero-indexed array A of N integers, returns the minimal positive integer (greater than 0) that does not occur in A.
For example, given:
  A[0] = 1
  A[1] = 3
  A[2] = 6
  A[3] = 4
  A[4] = 1
  A[5] = 2
the function should return 5.
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def solution(A):
    ''' Solve it with Pigeonhole principle.
        There are N integers in the input. So for the
        first N+1 positive integers, at least one of
        them must be missing.
    '''
    # We only care about the first N+1 positive integers.
    # occurrence[i] is for the integer i+1.
    occurrence = [False] * (len(A) + 1)
    for item in A:
        if 1 <= item <= len(A) + 1:
            occurrence[item-1] = True
    
    # Find out the missing minimal positive integer.
    for index in xrange(len(A) + 1):
        if occurrence[index] == False:
            return index + 1
    
    raise Exception("Should never be here.")
    return -1

https://github.com/yiqin/Codility-Practice/blob/master/MissingInteger.java
Space optimization:
    public int solution(int[] A) {
        int positiveCount = 0;      
        for(int i=0; i< A.length; i++) {
            positiveCount++;
        }
       
        int[] B = new int[positiveCount];
       
        for(int i=0; i<A.length; i++) {
            if(A[i]<=A.length && A[i]>0) {
                B[A[i]-1]=1;
            }
        }
       
        int min = B.length+1;
       
        for(int i=0; i<B.length; i++) {
            if(B[i]==0) {
                // min = B[i]+1;
                min = i+1;
                break;
            }
        }
       
        return min;
    }
http://www.martinkysel.com/codility-missinginteger-solution/
http://codility-lessons.blogspot.com/2014/07/lesson-2-missing-integers.html
Read full article from Solution to Missing-Integer by codility | Code Says

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