Number of Islands _ DFS.cpp

code/graph_algorithms/src/Number of Islands _ DFS.cpp

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+class Solution
+{
+private:
+    void dfsTraversal(int row, int col, vector<int> &delr, vector<int> &delc, vector<vector<char>> &grid, vector<vector<bool>> &vis)
+    {
+        // delr = {-1, 0, 1 ,0};
+        // delc = {0, -1, 0, 1};
+        vis[row][col] = true;
+        int total_rows = grid.size();
+        int total_columns = grid[0].size();
+        for (int i = 0; i < 4; i++)
+        {
+            int new_row = row + delr[i];
+            int new_col = col + delc[i];
+            if (new_row >= 0 && new_row < total_rows && new_col >= 0 && new_col < total_columns)
+            {
+                // checked validity of new row and new column
+                if (grid[new_row][new_col] == '1' && vis[new_row][new_col] == 0)
+                {
+                    dfsTraversal(new_row, new_col, delr, delc, grid, vis);
+                }
+            }
+        }
+    }
+    int solver(vector<vector<char>> &grid)
+    {
+        int total_rows = grid.size();
+        int total_columns = grid[0].size();
+        vector<vector<bool>> vis(total_rows, vector<bool>(total_columns, false));
+        int count = 0;
+        vector<int> delr = {-1, 0, 1, 0}; // change in row
+        vector<int> delc = {0, -1, 0, 1}; // change in column
+        // changes from one cell to another cell in 4 directions given by corresponding values at same index in delr and delc
+        for (int row = 0; row < total_rows; row++)
+        {
+            for (int col = 0; col < total_columns; col++)
+            {
+                if (grid[row][col] == '1' && vis[row][col] == false)
+                {
+                    count++;
+                    dfsTraversal(row, col, delr, delc, grid, vis);
+                }
+            }
+        }
+        return count;
+    }
+
+public:
+    int numIslands(vector<vector<char>> &grid)
+    {
+        // By the method of DFS
+        // Time Complexity of code: O(m*n)
+        // Auxillary Space Complexity of code: O(m*n)
+        int ans = solver(grid);
+        return ans;
+    }
+};