leetcode-287：寻找重复数

输入：nums = [1,3,4,2,2]
输出：2

输入：nums = [3,1,3,4,2]
输出：3

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