<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 Coor{
public:
    int x, y;
    Coor(int x, int y){
        this->x = x;
        this->y = y;
    }
};
int deltaX[4] = {0, 1, -1, 0};
int deltaY[4] = {1, 0, 0, -1};

class Solution {
public:
    int numIslands(vector<vector<char>>& grid) {
        if(grid.size() == 0 || grid[0].size() == 0) return 0;
        int islandCount = 0;
        int row = grid.size();
        int col = grid[0].size();

        vector<vector<bool>> visited(row, vector<bool> (col));
        for (int r = 0; r < row; r++){
            for (int c = 0; c < col; c++){
                if (grid[r][c] == '1' && !visited[r][c]){
                    bfs(r, c, grid, visited);
                    islandCount++;
                }
            }
        }

        return islandCount;
    }
private:
    void bfs(int r, int c, vector<vector<char>>& grid, vector<vector<bool>>& visited){
        queue<Coor*> q;
        Coor* co = new Coor(r, c);
        visited[r][c] = true;
        q.push(co);
        while (!q.empty()){
            Coor* cur = q.front();
            q.pop();
            for (int dir = 0; dir < 4; dir++){
                int newX = cur->x + deltaX[dir];
                int newY = cur->y + deltaY[dir];

                //cout << newX << " " << newY << " " << isValid(newX, newY, grid, visited) << endl;
                if (isValid(newX, newY, grid, visited)){
                    Coor* newCo = new Coor(newX, newY);
                    q.push(newCo);
                    visited[newX][newY] = true;
                }
            }

        }
    }

    bool isValid(int r, int c, vector<vector<char>>& grid, vector<vector<bool>>& visited){
        int row = grid.size();
        int col = grid[0].size();

        if (r < 0 || r >= row || c < 0 || c >= col) return false;
        if (visited[r][c] == true) return false;
        return grid[r][c] == '0' ? false : true;
    }

};
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