Find duplicate numbers.java

class Solution {
  public int findDuplicate(int[] nums) {
    int slow = nums[0];
    int 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;
  }
}