Finding missing elements in an array

Question

Given you have an array A[1..n] of size n, it contains elements from the set {1..n}. However, two of the elements are missing, (and perhaps two of the array elements are rep

Answer 1

Your solution isn't bad. Here's an alternative - Sort the list and iterate through it checking adjacent numbers. When there is a gap, print all the numbers in between. If k is the length of the array and n is the number to count to, we get O(k lg k + n) time, O(1) space