Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one.

Example 1:

Input: [1,3,4,2,2]
Output: 2

Example 2:

Input: [3,1,3,4,2]
Output: 3

Note:

• You must not modify the array (assume the array is read only).
• You must use only constant, O(1) extra space.
• Your runtime complexity should be less than O(n2).
• There is only one duplicate number in the array, but it could be repeated more than once.

Solution

var findDuplicate = function (nums) {
  let i = 0
  let store = {}
  while (i < nums.length) {
    if (store[nums[i]] !== undefined) {
      return nums[i]
    }
    else {
      store[nums[i]] = 0
    }
    i++
  }
};