287. Find the Duplicate Number.cpp

/******************
 *      
 *      Floyd's Tortoise and Hare (Cycle Detection)
 *
 *****************/

class Solution
{
public:
    int findDuplicate(vector<int> &nums)
    {
        int slow(nums[0]), fast(nums[0]);
        do
        {
            slow = nums[slow];
            fast = nums[nums[fast]];
        } while (slow != fast);
        fast = nums[0];
        while (slow != fast)
        {
            slow = nums[slow];
            fast = nums[fast];
        }
        return slow;
    }
};