Untitled

class Solution {
public:
    int findDuplicate(vector<int>& nums) {
        int fast=0,slow=0;
        while(1){
            slow=nums[slow];
            fast=nums[nums[fast]];
            if(slow==fast) break;
        }
        int slow1=0;
        int slow2=slow;
        while(slow1!=slow2){
            slow1=nums[slow1];
            slow2=nums[slow2];
        }
        return slow1;
    }
};