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*(*n*^{2}). - There is only one duplicate number in the array, but it could be repeated more than once.

**Solution:** We will solve this using Two pointers the brute force solution would be looping twice to find the duplicate which will take O(*n*^{2}).

```
class HackerHeap {
public int findDuplicate(int[] nums) {
int slow = 0;
int fast = 0;
do{
slow = nums[slow];
fast = nums[nums[fast]];
}while(slow!=fast);
int find =0;
while(find!=slow){
find = nums[find];
slow = nums[slow];
}
return find;
}
}
```