<p>Given an <code>m x n</code> 2D binary grid <code>grid</code> which represents a map of <code>&#39;1&#39;</code>s (land) and <code>&#39;0&#39;</code>s (water), return <em>the number of islands</em>.</p>

<p>An <strong>island</strong> is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> grid = [
  [&quot;1&quot;,&quot;1&quot;,&quot;1&quot;,&quot;1&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;1&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;]
]
<strong>Output:</strong> 1
</pre>

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

<pre>
<strong>Input:</strong> grid = [
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;1&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;1&quot;,&quot;0&quot;,&quot;0&quot;],
  [&quot;0&quot;,&quot;0&quot;,&quot;0&quot;,&quot;1&quot;,&quot;1&quot;]
]
<strong>Output:</strong> 3
</pre>

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

<ul>
	<li><code>m == grid.length</code></li>
	<li><code>n == grid[i].length</code></li>
	<li><code>1 &lt;= m, n &lt;= 300</code></li>
	<li><code>grid[i][j]</code> is <code>&#39;0&#39;</code> or <code>&#39;1&#39;</code>.</li>
</ul>

class Solution {
public:
    void bfs(vector<vector<char>> &grid, int row, int col) {
        grid[row][col] = '0';

        constexpr pair<int, int> delta[] = {
            {1, 0},
            {-1, 0},
            {0, 1},
            {0, -1},
        };

        for (const auto &[drow, dcol] : delta) {
            if (grid[row + drow][col + dcol] == '1') {
                bfs(grid, row + drow, col + dcol);
            }
        }
    }

    bool hasLand(vector<vector<char>> &grid) {
        for (int r = 0; r < grid.size(); r++) {
            for (int c = 0; c < grid[r].size(); c++) {
                if (grid[r][c] == '1')
                    return true;
            }
        }

        return false;
    }

    int numIslands(vector<vector<char>>& grid) {
        vector<vector<char>> padded(grid.size() + 2, vector<char>(grid[0].size() + 2));
        for (int r = 0; r < grid.size(); r++) {
            for (int c = 0; c < grid[0].size(); c++) {
                padded[r+1][c+1] = grid[r][c];
            }
        }

        int nislands = 0;

        for (int r = 0; r < padded.size(); r++) {
            for (int c = 0; c < padded[r].size(); c++) {
                if (padded[r][c] == '1') {
                    nislands++;
                    bfs(padded, r, c);
                }
            }
        }

        return nislands;
    }
};
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