class Solution {

public:
int duplicateInArray(vector<int>& nums) {
    int len = nums.size();
    int ele = len;
    for (int i=0;i<len;i++){
        int x = nums[i];
        if (x >= len || x < 0){
            return -1;
        }
    }
    for (int i=0;i<len;i++){

        while(1){
            int x = nums[i];
            if (x == i){
                break;
            }
            if (x != nums[x]  ){
                int temp = nums[i];
                nums[i] = nums[x] ;
                nums[x] = temp;
                continue;
            }
            else{
                return x;
            }
        }  
    }
    return -1;
}

};