Solution: Find the Duplicate Number

Statement

Given an array of positive numbers, nums, such that the values lie in the range $[1, n]$, inclusive, and that there are $n+1$ numbers in the array, find and return the duplicate number present in nums. There is only one repeated number in nums, but it may appear more than once in the array.

Note: You cannot modify the given array nums. You have to solve the problem using only constant extra space.

Constraints:

• $1 \leq n \leq 10^3$
• nums.length $= n + 1$
• $1 \leq$ nums[i] $\leq n$
• All the integers in nums are unique except for one integer that will appear more than once.

Solution