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

Answer 1

This solution gets 100/100 on the test:

class Solution {
    public int solution(int[] A) {

        int x = 0;
        while (x < A.length) {
            // Keep swapping the values into the matching array positions.
            if (A[x] > 0 && A[x] <= A.length && A[A[x]-1] != A[x])  {
                swap(A, x, A[x] - 1);
            } else {
                x++; // Just need to increment when current element and position match.
            }
        }

        for (int y=0; y < A.length; y++) {
            // Find first element that doesn't match position.
            // Array is 0 based while numbers are 1 based.
            if (A[y] != y + 1)  {
                return y + 1;
            }
        }

        return A.length + 1;
    }

    private void swap (int[] a, int i, int j) {
        int t = a[i];
        a[i] = a[j];
        a[j] = t;
    }
}