title: Finding first non-repeating number in integer array
body: <p>I got this question for an exam:</p>
  
  <blockquote>
    <p>Given an integer array find the first number which is not repeating in array using O(N) time complexity and O(1) space complexity.</p>
  </blockquote>
  
  <p>I couldn't think of any solution. I know I can iterate over the array and maintain a linkedhashmap which will store both array element and number of times it appears and then in the end I have to search hashmap to find that number. Space complexity is greater than O(1) but I couldn't think of other solution. </p>
  
  <p>I also read problem carefully and the said that max size of array would be 1million. I think if we can create a custom hashmap which will utilise an fixed size array of 1 million size then this can be achieved in O(1) space complexity as in that case storage required would be constant but nore sure if I am correct. Please let me know if there is any other solution. </p>