Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive. There is only one repeated number in nums, return this repeated number. You must solve the problem without modifying the array nums and using only constant extra space. Constraints: -> 1 <= n <= 10^5 -> nums.length == n + 1 -> 1 <= nums[i] <= n -> All the integers in nums appear only once except for precisely one integer which appears two or more times. Follow up: ->How can we prove that at least one duplicate number must exist in nums? ->Can you solve the problem in linear runtime complexity?