leetcode287.寻找重复数

与寻找链表环的起始点一样 ，用快慢指针让二者相遇后，慢指针回到起始点二者以同样速度移动最终会在环的起始点相遇

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