title: How can we find a repeated number in array in O(n) time and O(1) space complexity
body: <p>How can we find a repeated number in array in O(n) time and O(1) complexity?
  eg 
  array 2,1,4,3,3,10
  output is 3</p>
  
  <p>EDIT:
  I tried in following way.
  i found that if no is oddly repeated then we can achieve the result by doing xor . so i thought to make the element which is odd no repeating to even no and every evenly repeating no to odd.but for that i need to find out unique element array from input array in O(n) but couldn't find the way.</p>