<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:
    int n, m;
     bool valid(int ci, int cj) {
        if (ci < 0 || ci >= n || cj < 0 || cj >= m)
            return false;
        return true;
    }
    int islandPerimeter(vector<vector<int>>& grid) {
        int cnt = 0;
        n = grid.size();
        m = grid[0].size();
        bool vis[n][m];
        memset(vis, false, sizeof(vis));
        vector<pair<int, int>> d = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
        queue<pair<int, int>> q;
        int si = -1, sj = -1;
        for (int i = 0; i < n; i++) {
            for (int j = 0; j < m; j++) {
                if (!vis[i][j] && grid[i][j] == 1) {
                    si = i;
                    sj = j;
                    break;
                }
            }
        }
        q.push({si, sj});

        while (!q.empty()) {
            pair<int, int> p = q.front();
            int a = p.first;
            int b = p.second;
            q.pop();
            vis[a][b] = true;
            for (auto e : d) {
                int ci = a + e.first;
                int cj = b + e.second;
                if (valid(ci, cj)) {
                    if (grid[ci][cj] == 0)
                        cnt++;
                    if (!vis[ci][cj] && grid[ci][cj] == 1) {
                        q.push({ci, cj});
                        vis[ci][cj] = true;
                    }
                } else {
                    cnt++;
                }
            }
        }
        return cnt;
    }
};
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