<p>The string <code>&quot;PAYPALISHIRING&quot;</code> 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>

<pre>
P   A   H   N
A P L S I I G
Y   I   R
</pre>

<p>And then read line by line: <code>&quot;PAHNAPLSIIGYIR&quot;</code></p>

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

<pre>
string convert(string s, int numRows);
</pre>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;PAYPALISHIRING&quot;, numRows = 3
<strong>Output:</strong> &quot;PAHNAPLSIIGYIR&quot;
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;PAYPALISHIRING&quot;, numRows = 4
<strong>Output:</strong> &quot;PINALSIGYAHRPI&quot;
<strong>Explanation:</strong>
P     I    N
A   L S  I G
Y A   H R
P     I
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> s = &quot;A&quot;, numRows = 1
<strong>Output:</strong> &quot;A&quot;
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= s.length &lt;= 1000</code></li>
	<li><code>s</code> consists of English letters (lower-case and upper-case), <code>&#39;,&#39;</code> and <code>&#39;.&#39;</code>.</li>
	<li><code>1 &lt;= numRows &lt;= 1000</code></li>
</ul>

class Solution {
public:
    string convert(string s, int numRows) {
        std::string result_str = "";
        std::unordered_map<std::string,char> ch_row_column; 
        int cur_row = 0, cur_column = 0;      //  row and column of the current character

        if (numRows==1||s.size()==1)
            return s;
        else if (numRows>=s.size())
            return s;

        for (int i = 0; i<s.size(); i++){
            if (cur_column%(numRows-1)==0){                  // odd column
                ch_row_column.insert({std::to_string(cur_row++)+','+std::to_string(cur_column),s[i]});
                if (cur_row%numRows==0 && cur_row!=0){
                    cur_column++;
                    if (cur_column%(numRows-1)==0)
                        cur_row = 0;
                    else
                        cur_row--;
                }
            }
            else{                                // even column
                ch_row_column.insert({std::to_string(--cur_row)+','+std::to_string(cur_column),s[i]});
                cur_column++;
                if (cur_column%(numRows-1)==0 && cur_column!=0)
                    cur_row--;
            }   
        }

        int max_column = cur_column;       // record the maximum column number

        cur_column = 0;
        cur_row    = 0;

        for (int i = 0; i<s.size(); i++){
            if (ch_row_column[{std::to_string(cur_row)+','+std::to_string(cur_column)}]=='\0'){
                cur_column = 0;
                cur_row++;
                i--;
                continue;
            }
            result_str += ch_row_column[{std::to_string(cur_row)+','+std::to_string(cur_column)}];

            if (cur_column<max_column && cur_column%(numRows-1)==0 && cur_row!=(numRows-1))          
                cur_column = cur_column + (numRows - 1 - cur_row);
            else if (cur_column<max_column)
                cur_column = cur_column + cur_row;
            else {
                cur_column = 0;
                cur_row++;
            }
        }

        return result_str;
    }
};
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