Create 200. Number of Islands.cpp

200. Number of Islands.cpp

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+class Solution {
+private:
+    void bfs(int r, int c, vector<vector<char>>& grid, vector<vector<bool> >&vis)
+    {
+        vis[r][c] = 1;
+
+        queue<pair<int, int> > q;
+        q.push({r, c});
+
+        int n = grid.size();
+        int m = grid[0].size();
+
+        while(!q.empty())
+        {
+            int row = q.front().first;
+            int col = q.front().second;
+            q.pop();
+
+            //traverse all it's neighbours and mark them if it's a land
+            if(row-1 >= 0 && !vis[row-1][col] && grid[row-1][col] == '1')
+            {
+               q.push({row-1, col});
+               vis[row-1][col] = 1;
+            }
+            if(row+1 < n && !vis[row+1][col] && grid[row+1][col] == '1')
+            {
+               q.push({row+1, col});
+               vis[row+1][col] = 1; 
+            }
+            if(col-1 >= 0 && !vis[row][col-1] && grid[row][col-1] == '1')
+            {
+                q.push({row, col-1});
+                vis[row][col-1] = 1;
+            }
+            if(col+1 < m && !vis[row][col+1] && grid[row][col+1] == '1')
+            {
+                q.push({row, col+1});
+                vis[row][col+1] = 1;
+            }
+        }
+    }
+public:
+    int numIslands(vector<vector<char>>& grid) {
+        int n = grid.size();
+        int m = grid[0].size();
+
+        vector<vector<bool> > vis (n, vector<bool>(m, 0));
+
+        int cnt = 0;
+
+        for(int i=0; i<n; i++){
+            for(int j=0; j<m; j++){
+                if(!vis[i][j] && grid[i][j] == '1')
+                {
+                    cnt++;
+                    bfs(i, j, grid, vis);
+                }
+            }
+        }
+
+    return cnt;
+
+    }
+
+};