21. Reverse Coding

The problem can be found at the following link: Question Link

My Approach

To solve this problem, I have used a simple approach based on the formula for the sum of natural numbers.

• The formula (n*(n+1))/2 gives the sum of the first n natural numbers.

• In the given code, I calculate the sum using this formula and return the result.

Time and Auxiliary Space Complexity

• Time Complexity: O(1) since the calculation of the sum of natural numbers can be done in constant time.

• Auxiliary Space Complexity: O(1) as there is no extra space used that scales with the input.

Code (C++)

class Solution {
public:
    int mod = 1e9 + 7;
    int sumOfNaturals(int n) {
        long long sum = n;
        sum = (sum * (sum + 1)) % mod;
        sum /= 2;
        
        return sum;
    }
};

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