<p>You are given an <code>m x n</code> binary matrix <code>grid</code>, where <code>0</code> represents a sea cell and <code>1</code> represents a land cell.</p>

<p>A <strong>move</strong> consists of walking from one land cell to another adjacent (<strong>4-directionally</strong>) land cell or walking off the boundary of the <code>grid</code>.</p>

<p>Return <em>the number of land cells in</em> <code>grid</code> <em>for which we cannot walk off the boundary of the grid in any number of <strong>moves</strong></em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/18/enclaves1.jpg" style="width: 333px; height: 333px;" />
<pre>
<strong>Input:</strong> grid = [[0,0,0,0],[1,0,1,0],[0,1,1,0],[0,0,0,0]]
<strong>Output:</strong> 3
<strong>Explanation:</strong> There are three 1s that are enclosed by 0s, and one 1 that is not enclosed because its on the boundary.
</pre>

<p><strong class="example">Example 2:</strong></p>
<img alt="" src="https://assets.leetcode.com/uploads/2021/02/18/enclaves2.jpg" style="width: 333px; height: 333px;" />
<pre>
<strong>Input:</strong> grid = [[0,1,1,0],[0,0,1,0],[0,0,1,0],[0,0,0,0]]
<strong>Output:</strong> 0
<strong>Explanation:</strong> All 1s are either on the boundary or can reach the boundary.
</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;= 500</code></li>
	<li><code>grid[i][j]</code> is either <code>0</code> or <code>1</code>.</li>
</ul>

class Solution {
public:

    void markAllBoundaryConnected(vector<vector<int>> & grid){
        int n = grid.size(),  m = grid[0].size();
        queue<int> que;
        vector<vector<int>> dir = {{-1,0},{1,0}, {0, 1}, {0, -1}};
        
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                if(i == 0 || j == 0 || i == n - 1 || j == m - 1){
                    if(grid[i][j] == 1){
                        grid[i][j] = 0;
                        que.push(i * m + j);
                    }
                }
            }
        }


        while(que.size() != 0){
            int size = que.size();
            while(size-- > 0){
                int ridx = que.front(); que.pop();
                int r = ridx / m;
                int c = ridx % m;

                for(vector<int> & d : dir){
                    int x = r + d[0];
                    int y = c + d[1];
                    if(x >= 0 && y >= 0 && x < n && y < m && grid[x][y] == 1){
                        grid[x][y] = 0;
                        que.push(x * m + y);
                    }
                }
            }
        }
    }

    int countAllUnconnectedGrid(vector<vector<int>> &grid){
        int n = grid.size(),  m = grid[0].size();
        int count = 0;
        for(int i = 0; i < n; i++){
            for(int j = 0; j < m; j++){
                    if(grid[i][j] == 1)
                        count++;
            }
        }

        return count;
    }

    int numEnclaves(vector<vector<int>>& grid) {
        markAllBoundaryConnected(grid);
        return countAllUnconnectedGrid(grid);
    }
};
27492