LC 287. Find the Duplicate Number

link

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