# Find the Duplicate Number Leetcode Solution

## Find the Duplicate Number Leetcode Problem :

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 uses only constant extra space.

## Find the Duplicate Number Leetcode Solution :

### Constraints :

• 1 <= n <= 105
• 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.

### Example 1:

• Input: nums = [3,1,3,4,2]
• Output: 3

Intuition :

We use the linked list by using the technique to find cycle in the list. The element to which both the pointers meet will be the element repeated in the list.

Approach :

We start by initializing a slow pointer and a fast pointer and then move the fast pointer with 2x the speed of the slow pointer until they both point to the same element. To prevent any bottlenecks or overflows we initialize the fast pointer again to the first element of the list and then again moveboth the pointers with the same speed to end with the repeated element.

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