Number of Islands _ DFS.cpp

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

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+#include <bits/stdc++.h>
+using namespace std;
+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:
+    Solution(vector<vector<char>> &grid)
+    {
+        // constructor created
+    }
+    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)
+        // LeetCode link: https://leetcode.com/problems/number-of-islands/description/
+
+        // Sample Input 1 (for LeetCode): [["1","1","1","1","0"],["1","1","0","1","0"],["1","1","0","0","0"],["0","0","0","0","0"]]
+        /*
+        In the sample input, "1" represents a land piece, and "0" represents a water area.
+        The grid is a m*n matrix with m rows and n columns, here, m being 4 and n being 5.
+        The grid is in the form of a 2D array/vector in the input as given above.
+        Visualizing the input more effectively,
+        [
+        ["1","1","1","1","0"],
+        ["1","1","0","1","0"],
+        ["1","1","0","0","0"],
+        ["0","0","0","0","0"]
+        ]
+        */
+
+        /* Sample Input 2 (for terminal): [["1","1","1","1","0"],["1","1","0","1","0"],["1","1","0","0","0"],["0","0","0","0","0"]]
+        4 5
+        1 1 1 1 0
+        1 1 0 1 0
+        1 1 0 0 0
+        0 0 0 0 0
+        */
+        /*
+        In the sample input, the first line has two integers: m and n.
+        m represents the number of rows and n represents the number of columns.
+        1 represents a land piece, and 0 represents a water area.
+        The grid is a m*n matrix with m rows and n columns, here, m being 4 and n being 5.
+        The grid is in the form of a 2D array/vector in the input as given above.
+        */
+
+        int ans = solver(grid);
+        return ans;
+    }
+};
+
+int main()
+{
+    // Number_of_Islands
+    //  LeetCode link: https://leetcode.com/problems/number-of-islands/description/
+    int m, n;
+    cout << "Number of rows and columns: ";
+    cin >> m >> n;
+    vector<vector<char>> grid(m, vector<char>(n));
+    cout << "The grid: " << endl;
+    for (int i = 0; i < m; i++)
+    {
+        for (int j = 0; j < n; j++)
+        {
+            cin >> grid[i][j];
+        }
+    }
+
+    Solution soln(grid);
+    int solution = soln.numIslands(grid);
+    cout << "The number of Islands: " << solution << endl;
+    return 0;
+}