287.Find the Duplicate Number

1- Slow Fast, Find Cycle

https://leetcode.com/problems/find-the-duplicate-number/discuss/72846/

class Solution {
    public int findDuplicate(int[] nums) {
        if(nums.length > 1){
            int slow = nums[0];
            int fast = nums[nums[0]];
            while(slow != fast){
                slow = nums[slow];
                fast = nums[nums[fast]];
            }
            slow = 0;
            while(slow != fast){
                slow = nums[slow];
                fast = nums[fast];
            }
            return slow;
        }
        return -1;
    }
}