text: // Given an array containing n distinct numbers taken from 0, 1, 2, ..., n, find the one that is missing from the array.
  
  // Example 1:
  
  // Input: [3,0,1]
  // Output: 2
  // Example 2:
  
  // Input: [9,6,4,2,3,5,7,0,1]
  // Output: 8
  // Note:
  // Your algorithm should run in linear runtime complexity. Could you implement it using only constant extra space complexity?
  
  /**
   * @param {number[]} nums
   * @return {number}
   */
   
  // O(n) time, O(1) space
  // Gauss formular for sum from 0 to n: totalSum = (n * (n + 1))/2
  var missingNumber = function(nums) {
      var expectedSum = (nums.length * (nums.length + 1)) / 2;
      var actualSum = 0;
      var missingInt;
      
      for(var val of nums) {
          actualSum += val;
      }
      
      missingInt = expectedSum - actualSum;
      
      return missingInt;
  };