<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) {
        const size_t N(s.size());
        if (numRows == 1)
            return s;
        int cols(0), idx(0);
        bool isCross(false);
        while (idx < N) {
            if (isCross) {
                idx += (numRows - 2);
                cols += (numRows - 2);
                isCross = !isCross;
            } else {
                idx += numRows;
                cols += 1;
                isCross = !isCross;
            }
        }

        vector<vector<char>> result(numRows, vector<char>(cols, 0));
        idx = 0;
        int row = 0, col = 0;
        isCross = false;
        while (idx < N) {
            result[row][col] = s[idx++];
            if (!isCross) {
                if (row == numRows - 1) {
                    isCross = true;
                    row = row - 1;
                    col = col + 1;
                } else {
                    row = row + 1;
                }
            } else {
                if (row == 0) {
                    isCross = false;
                    row = row + 1;
                } else {
                    row = row - 1;
                    col = col + 1;
                }
            }
        }
        string zigzag;
        for (int i = 0; i < numRows; i++) {
            for (int j = 0; j < cols; j++) {
                if (result[i][j] != 0) {
                    zigzag += (result[i][j]);
                }
            }
        }
        return zigzag;
    }
};
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