Create LargestIslandGraph.cpp

Cpp/LargestIslandGraph.cpp

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+#include <bits/stdc++.h>
+using namespace std;
+
+#define ROW 5
+#define COL 5
+
+// A function to check if a given
+// cell (row, col) can be included in DFS
+int isSafe(int M[][COL], int row, int col,
+           bool visited[][COL])
+{
+    // row number is in range, column
+    // number is in range and value is 1
+    // and not yet visited
+    return (row >= 0) && (row < ROW) && (col >= 0) && (col < COL) && (M[row][col] && !visited[row][col]);
+}
+
+// A utility function to do DFS for a
+// 2D boolean matrix. It only considers
+// the 8 neighbours as adjacent vertices
+void DFS(int M[][COL], int row, int col,
+         bool visited[][COL])
+{
+    // These arrays are used to get
+    // row and column numbers of 8
+    // neighbours of a given cell
+    static int rowNbr[] = { -1, -1, -1, 0, 0, 1, 1, 1 };
+    static int colNbr[] = { -1, 0, 1, -1, 1, -1, 0, 1 };
+
+    // Mark this cell as visited
+    visited[row][col] = true;
+
+    // Recur for all connected neighbours
+    for (int k = 0; k < 8; ++k)
+        if (isSafe(M, row + rowNbr[k], col + colNbr[k], visited))
+            DFS(M, row + rowNbr[k], col + colNbr[k], visited);
+}
+
+// The main function that returns
+// count of islands in a given boolean
+// 2D matrix
+int countIslands(int M[][COL])
+{
+    // Make a bool array to mark visited cells.
+    // Initially all cells are unvisited
+    bool visited[ROW][COL];
+    memset(visited, 0, sizeof(visited));
+
+    // Initialize count as 0 and
+    // traverse through the all cells of
+    // given matrix
+    int count = 0;
+    for (int i = 0; i < ROW; ++i)
+        for (int j = 0; j < COL; ++j)
+
+            // If a cell with value 1 is not
+            if (M[i][j] && !visited[i][j]) {
+                // visited yet, then new island found
+                // Visit all cells in this island.
+                DFS(M, i, j, visited);
+
+                // and increment island count
+                ++count;
+            }
+
+    return count;
+}
+
+// Driver code
+int main()
+{
+    int M[][COL] = { { 1, 1, 0, 0, 0 },
+                     { 0, 1, 0, 0, 1 },
+                     { 1, 0, 0, 1, 1 },
+                     { 0, 0, 0, 0, 0 },
+                     { 1, 0, 1, 0, 1 } };
+
+    cout << "Number of islands is: " << countIslands(M);
+
+    return 0;
+}