Leetcode Zigzag Conversion problem solution in C++ programming

In the Leetcode Zigzag Conversion problem solution in C++ programming The string “PAYPALISHIRING” is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)

P A H N
A P L S I I G
Y I R
And then read line by line: “PAHNAPLSIIGYIR”

Write the code that will take a string and make this conversion given a number of rows:

string convert(string s, int numRows);

Leetcode Zigzag Conversion problem solution in C++ programming

class Solution {
public:
    string convert(string s, int num_rows) {
        if (num_rows == 1)
            return s;
        string res;
        vector<string> mat(num_rows, "");

        downstate(0, 0, num_rows, s, mat);
        
        for (string e : mat)
            for (char ch : e )
                res.push_back(ch);

        return res;
    }

private:
    void downstate(int i, int row, const size_t num_rows, string input, vector<string>& mat){
        if (i == input.size())
            return;

        char ch = input[i];
        mat[row].push_back(ch);
        
        if (row == num_rows-1)
            upstate(i+1, row-1, num_rows, input, mat);
        else
            downstate(i+1, row+1, num_rows, input, mat);
    }

    void upstate(int i, int row, const size_t num_rows, string input, vector<string>& mat){
        if (i == input.size())
            return;
        
        char ch = input[i];
        mat[row].push_back(ch);

        if (row == 0)
            downstate(i+1, row+1, num_rows, input, mat);
        else
            upstate(i+1, row-1, num_rows, input, mat);
    }
};

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By Neha Singhal

Hi, my name is Neha singhal a software engineer and coder by profession. I like to solve coding problems that give me the power to write posts for this site.

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