<p>Given an <code>m x n</code> matrix <code>mat</code>, return <em>an array of all the elements of the array in a diagonal order</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/04/10/diag1-grid.jpg" style="width: 334px; height: 334px;" />
<pre>
<strong>Input:</strong> mat = [[1,2,3],[4,5,6],[7,8,9]]
<strong>Output:</strong> [1,2,4,7,5,3,6,8,9]
</pre>

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

<pre>
<strong>Input:</strong> mat = [[1,2],[3,4]]
<strong>Output:</strong> [1,2,3,4]
</pre>

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

<ul>
	<li><code>m == mat.length</code></li>
	<li><code>n == mat[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 10<sup>4</sup></code></li>
	<li><code>1 &lt;= m * n &lt;= 10<sup>4</sup></code></li>
	<li><code>-10<sup>5</sup> &lt;= mat[i][j] &lt;= 10<sup>5</sup></code></li>
</ul>

class Solution {
private:
  vector<int> ans;
public:
    vector<int> findDiagonalOrder(vector<vector<int>>& mat) {
         if(mat.empty())
        {
            return ans;
        }
        int row = mat.size();
        int column = mat[0].size();
        int i = 0;
        int j = 0;
        int index = 0;
        
        bool flag = true;
        while(i < row && j < column)
        {
            if(flag == true)
            {
                while(i > 0 && j < column-1)
                {
                    ans.push_back(mat[i][j]);
                    i--;
                    j++;
                }
                ans.push_back(mat[i][j]);
                if(j == column-1)
                {
                    i++;
                }
                else
                {
                    j++;
                }
            }
            else
            {
                    while(i < row-1 && j > 0)
                    {
                        ans.push_back(mat[i][j]);
                        i++;
                        j--;
                    }
                    ans.push_back(mat[i][j]);
                    if(i == row-1)
                    {
                        j++;
                    }
                    else
                    {
                        i++;
                    }
            
            }
            flag = !flag;
        }
        return ans;
    }
};
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