Question1.cpp

// Here I started My Journey with the questions :->

1 -> Find the Duplicate Number

Solution :

class Solution {
public:
    int findDuplicate(vector<int>& nums) {
        sort(nums.begin(),nums.end());
        for(int i=0;i<nums.size();i++){
           if(nums[i]==nums[i+1])return nums[i];
        }
        return 0;
    }
};

Another Aproach using Fast And Slow Pointer 

class Solution {
public:
    int findDuplicate(std::vector<int>& nums) {
        int slow = nums[0];
        int fast = nums[0];

        // Find the intersection point of the two pointers
        do {
            slow = nums[slow];
            fast = nums[nums[fast]];
        } while (slow != fast);

        // Find the entrance of the cycle
        slow = nums[0];
        while (slow != fast) {
            slow = nums[slow];
            fast = nums[fast];
        }

        return slow;
    }
};