Problem Statement

We are given an unsorted array containing n+1 numbers taken from the range 1 to n. The array has only one duplicate but it can be repeated multiple times. Find that duplicate number without using any extra space. You are, however, allowed to modify the input array.

Example 1:

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

Example 2:

Input: [2, 1, 3, 3, 5, 4]
Output: 3

Example 3:

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

Constraints:

• nums.length == n + 1
• 1 <= n <= 10^5
• 1 <= nums[i] <= n
• All the integers in nums appear only once except for precisely one integer which appears two or more times.

Try it yourself

Try solving this question here: