<p>You are given <code>row x col</code> <code>grid</code> representing a map where <code>grid[i][j] = 1</code> represents&nbsp;land and <code>grid[i][j] = 0</code> represents water.</p>

<p>Grid cells are connected <strong>horizontally/vertically</strong> (not diagonally). The <code>grid</code> is completely surrounded by water, and there is exactly one island (i.e., one or more connected land cells).</p>

<p>The island doesn&#39;t have &quot;lakes&quot;, meaning the water inside isn&#39;t connected to the water around the island. One cell is a square with side length 1. The grid is rectangular, width and height don&#39;t exceed 100. Determine the perimeter of the island.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img src="https://assets.leetcode.com/uploads/2018/10/12/island.png" style="width: 221px; height: 213px;" />
<pre>
<strong>Input:</strong> grid = [[0,1,0,0],[1,1,1,0],[0,1,0,0],[1,1,0,0]]
<strong>Output:</strong> 16
<strong>Explanation:</strong> The perimeter is the 16 yellow stripes in the image above.
</pre>

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

<pre>
<strong>Input:</strong> grid = [[1]]
<strong>Output:</strong> 4
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> grid = [[1,0]]
<strong>Output:</strong> 4
</pre>

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

<ul>
	<li><code>row == grid.length</code></li>
	<li><code>col == grid[i].length</code></li>
	<li><code>1 &lt;= row, col &lt;= 100</code></li>
	<li><code>grid[i][j]</code> is <code>0</code> or <code>1</code>.</li>
	<li>There is exactly one island in <code>grid</code>.</li>
</ul>

class Solution:
    def islandPerimeter(self, grid: List[List[int]]) -> int:
        g=[] #matrix stores the continous horizontal ones.
        for r in range(len(grid)):
            count = 0
            a = []
            for c in range(len(grid[0])-1, -1, -1):
                if grid[r][c]:
                    count+=grid[r][c]
                    a.insert(0, count)
                else:
                    count = 0
                    a.insert(0, 0)
            g.append(a.copy())

        for c in range(len(grid[0])): #grid stores the continous vertical ones.
            for r in range(len(grid)-2, -1, -1):
                if grid[r][c]:
                    grid[r][c] += grid[r+1][c]
        ans = 0
        row = 0
        while row < len(g): #computing left-right edges
            col = 0
            while col < len(g[0]):
                if g[row][col]:
                    ans+=2
                    col+=g[row][col]
                else:
                    col+=1
            row+=1

        col = 0
        while col < len(grid[0]): #computing top-bottom edges
            row = 0
            while row < len(grid):
                if grid[row][col]:
                    ans += 2
                    row += grid[row][col]
                else:
                    row+=1
            col+=1
        return ans
16766