<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 {
public:
    vector<int> findDiagonalOrder(vector<vector<int>>& mat) {
        vector<int>ans;
        int n=mat.size();
        int m=mat[0].size();
        bool flag=true;
        for(int j=0;j<m;j++)
        {
            int i=0;
            int k=j;
            if(flag)
            {
                vector<int>temp;
                while(i>=0&&i<n&&k>=0&&k<m)
                {
                    temp.push_back(mat[i][k]);
                    i++;k--;
                }
                for(int i=temp.size()-1;i>=0;i--)
                ans.push_back(temp[i]);
                flag=!flag;
            }
            else 
            {
                while(i>=0&&i<n&&k>=0&&k<m)
                {
                    ans.push_back(mat[i][k]);
                    i++;k--;
                }
                flag=!flag;
            }
        }
        for(int j=1;j<n;j++)
        {
            int k=m-1;
            int i=j;
            if(flag)
            {
                vector<int>temp;
                while(i>=0&&i<n&&k>=0&&k<m)
                {
                    temp.push_back(mat[i][k]);
                    i++;k--;
                }
                for(int i=temp.size()-1;i>=0;i--)
                ans.push_back(temp[i]);
                flag=!flag;
            }
            else 
            {
                while(i>=0&&i<n&&k>=0&&k<m)
                {
                    ans.push_back(mat[i][k]);
                    i++;k--;
                }
                flag=!flag;
            }
        }
        return ans;
    }
};
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