<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:
    bool movement = true;
    vector<int> findDiagonalOrder(vector<vector<int>>& mat) {
        vector<int> result;
        if (mat.size() == 0)
            return result;
        int m = mat.size();
        int n = mat[0].size();

        int x = 0; int y =0;
        result.push_back(mat[x][y]);
        while ((x != m-1) || (y != n-1)) {
            vector<int> nextposition = findNextValidPosition(x , y, m , n);
            x = nextposition[0];
            y = nextposition[1];
            result.push_back(mat[x][y]);
        }
        return result;
        
    }

    vector<int> findNextValidPosition(int x , int y , int m, int n) {
        if (movement && isInbound(x-1,y+1,m,n))
            return vector<int>{x-1, y+1};
        if (!movement && isInbound(x+1,y-1,m,n))
           return vector<int>{x+1, y-1};

        vector<int> nextPosition;
        if (movement) {
            if (isInbound(x, y+1, m,n))
                nextPosition = {x, y+1};
            else if(isInbound(x + 1, y, m,n))
                nextPosition = {x + 1, y};
            movement = false;
        }
        else {
            if (isInbound(x + 1, y, m,n))
                nextPosition = {x+1, y};
            else if(isInbound(x, y+1, m,n))
                nextPosition = {x, y+1};
            movement = true;
        }
        
        return nextPosition;
    }

    bool isInbound(int x , int y , int m, int n) {
        if ( x >= 0 && x < m && y >= 0 && y < n)
            return true;
        return false;
    }


};
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