<p>An <strong>image smoother</strong> is a filter of the size <code>3 x 3</code> that can be applied to each cell of an image by rounding down the average of the cell and the eight surrounding cells (i.e., the average of the nine cells in the blue smoother). If one or more of the surrounding cells of a cell is not present, we do not consider it in the average (i.e., the average of the four cells in the red smoother).</p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/05/03/smoother-grid.jpg" style="width: 493px; height: 493px;" />
<p>Given an <code>m x n</code> integer matrix <code>img</code> representing the grayscale of an image, return <em>the image after applying the smoother on each cell of it</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/05/03/smooth-grid.jpg" style="width: 613px; height: 253px;" />
<pre>
<strong>Input:</strong> img = [[1,1,1],[1,0,1],[1,1,1]]
<strong>Output:</strong> [[0,0,0],[0,0,0],[0,0,0]]
<strong>Explanation:</strong>
For the points (0,0), (0,2), (2,0), (2,2): floor(3/4) = floor(0.75) = 0
For the points (0,1), (1,0), (1,2), (2,1): floor(5/6) = floor(0.83333333) = 0
For the point (1,1): floor(8/9) = floor(0.88888889) = 0
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/05/03/smooth2-grid.jpg" style="width: 613px; height: 253px;" />
<pre>
<strong>Input:</strong> img = [[100,200,100],[200,50,200],[100,200,100]]
<strong>Output:</strong> [[137,141,137],[141,138,141],[137,141,137]]
<strong>Explanation:</strong>
For the points (0,0), (0,2), (2,0), (2,2): floor((100+200+200+50)/4) = floor(137.5) = 137
For the points (0,1), (1,0), (1,2), (2,1): floor((200+200+50+200+100+100)/6) = floor(141.666667) = 141
For the point (1,1): floor((50+200+200+200+200+100+100+100+100)/9) = floor(138.888889) = 138
</pre>

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

<ul>
	<li><code>m == img.length</code></li>
	<li><code>n == img[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 200</code></li>
	<li><code>0 &lt;= img[i][j] &lt;= 255</code></li>
</ul>

class Solution {
    
    // if cell exist return its values otherwise -1.
    int getValueOfCell(vector<vector<int>>& img, int i, int j, int n, int m) {
        if(i<0 || j<0 || i>=n || j>=m) {
            return -1;
        }
        return img[i][j];
    }

    //Find Average of each cell
    int getAverageOfCell(vector<vector<int>>& img, int row, int cell, int n, int m) {
        int cntOfValidCell = 0, Sum=0; // contain count and sum of calculating average.

        // Iterate over each neighbour of cell and find its value.
        for(int i=-1;i<=1;i++) {
            for(int j=-1;j<=1;j++) {
                int searchRow = row+i, searchCell = cell+j;
                int val = getValueOfCell(img,searchRow,searchCell,n,m);
                if(val!=-1){
                    Sum+=val;
                    cntOfValidCell++;
                }
            }
        }

        return Sum/cntOfValidCell; // return average
    }

public:
    vector<vector<int>> imageSmoother(vector<vector<int>>& img) {

        int n=img.size();      //Row Size
        int m=img[0].size();  //Column Size
        vector<vector<int>> ans(n);

        for(int i=0;i<n;i++) {
            for(int j=0;j<m;j++) {
                int val = getAverageOfCell(img, i, j, n, m); //Find Average of each cell
                ans[i].push_back(val);
            }
        }

        return ans;
        
    }
};
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