26. Print Pattern

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

My Approach

To make this pattern, I followed a recursive technique with backtracking.

• I kept reducing N by 5 in a loop until it got to 0 or less.

• While doing this, I added the current N value to the output vector twice. Once before making the recursive call and once after.

• The pattern comes from the sequence of values added to the vector.

Time and Auxiliary Space Complexity

• Time Complexity: O(N), where N is the input integer.

• Auxiliary Space Complexity: O(N), as we store the pattern in a vector.

Code (C++)

class Solution {
public:
    void solve(int n, vector<int>& out) {
        out.push_back(n);
        if (n <= 0)
            return;
        solve(n - 5, out);
        out.push_back(n);
    }

    vector<int> pattern(int N) {
        vector<int> out;
        solve(N, out);
        return out;
    }
};

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