<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 {
public:
    vector<vector<int>> gGrid;
    bool visited[101][101];
    int dr[4] = {1, 0, -1, 0};
    int dc[4] = {0, 1, 0, -1};
    bool isValid(int r, int c) {
        if (r < 0 || r >= gGrid.size() || c < 0 || c >= gGrid[r].size()) return false;
        return true;
    }

    int solve(int r, int c) {
        int ret = 0;

        visited[r][c] = true;
        for (int i = 0; i < 4; i++) {
            int nr = r + dr[i];
            int nc = c + dc[i];
            if (isValid(nr, nc) && gGrid[nr][nc] == 1) {
                if (!visited[nr][nc]) {
                    ret += solve(nr, nc);
                }
            } else {
                ret++;
            }
        }

        return ret;
    }
    int islandPerimeter(vector<vector<int>>& grid) {
        gGrid = grid;
        int ret = 0;
        bool f = false;
        for (int i = 0; !f && i < gGrid.size(); i++) {
            for (int j = 0; j < gGrid[i].size(); j++) {
                if (gGrid[i][j] == 1) {
                    f = true;
                    ret = solve(i, j);
                    break;
                }
            }
        }
        return ret;
    }
};
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