<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:
    int numEnclaves(vector<vector<int>>& grid) {
        int result = 0;

        for(int i = 0; i < grid.size(); i++) {
            for(int j = 0; j < grid[i].size(); j++) {
                // Sea cell
                if(grid[i][j] == 0) {
                    continue;
                }

                bool boundaryNodeReached = false;

                int numDiscoveredNodes = bfs(grid, i, j, boundaryNodeReached);

                if(!boundaryNodeReached) {
                    result += numDiscoveredNodes;
                }
            }
        }

        return result;
    }

    int bfs(vector<vector<int>>& grid, int row, int column, bool& boundaryNodeReached) {
        int numNodesDiscovered = 0;

        queue<pair<int, int>> q;
        q.push(make_pair(row, column));

        while(!q.empty()) {
            pair<int, int> entry = q.front();
            q.pop();

            int currentRow = get<0>(entry);
            int currentColumn = get<1>(entry);

            if(currentRow < 0 || currentRow >= grid.size() || currentColumn < 0 || currentColumn >= grid[0].size()) {
                continue;
            }

            if(grid[currentRow][currentColumn] == 0) {
                continue;
            }

            grid[currentRow][currentColumn] = 0;
            numNodesDiscovered++;

            if(currentRow == 0 || currentRow == grid.size() - 1 || currentColumn == 0 || currentColumn == grid[0].size() - 1) {
                boundaryNodeReached = true;
            }

            q.push(make_pair(currentRow + 1, currentColumn));
            q.push(make_pair(currentRow - 1, currentColumn));
            q.push(make_pair(currentRow, currentColumn + 1));
            q.push(make_pair(currentRow, currentColumn - 1));
        }

        return numNodesDiscovered;
    }
};
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