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Number of Islands in a 2D Grid

Certification: Intermediate Level Accuracy: 0% Submissions: 0 Points: 12

Write a C# program to implement the numberOfIslands(char[][] grid) function, which counts the number of islands in a 2D grid. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are surrounded by water.

Example 1
    
  
  • Input: grid = [

     ['1','1','0','0','0'],

     ['1','1','0','0','0'],

     ['0','0','1','0','0'],

     ['0','0','0','1','1']
]
    • 
  
  • Output: 3
    • 
  
  • Explanation: 
    
      
      
    • The grid has 3 islands.
      • 
      
    • The first island is formed by the first two rows, first two columns.
      • 
      
    • The second island is formed by the single '1' in the third row, third column.
      • 
      
    • The third island is formed by the two '1's in the fourth row, fourth and fifth columns.
      • 
    
    
  
    •
Example 2
    
  
  • Input: grid = [

     ['1','1','1','1','0'],

     ['1','1','0','1','0'],

     ['1','1','0','0','0'],

     ['0','0','0','0','0']
]
    • 
  
  • Output: 1
    • 
  
  • Explanation: 
    
      
      
    • There is only one island formed by all the '1's that are connected horizontally or vertically.
      • 
    
    
  
    •
Constraints
    
  
  • 1 ≤ grid.length, grid[i].length ≤ 300
    • 
  
  • grid[i][j] is either '0' or '1'
    • 
  
  • Time Complexity: O(m * n) where m is the number of rows and n is the number of columns
    • 
  
  • Space Complexity: O(m * n)
    •
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Hint
Solution

Solution Hints

    
  
  • Use Depth-First Search (DFS) or Breadth-First Search (BFS) to traverse the grid
    • 
  
  • Mark visited cells to avoid counting the same island multiple times
    • 
  
  • When you find a '1', increment the count and perform DFS/BFS to mark all connected '1's as visited
    • 
  
  • Remember to only move in four directions: up, down, left, and right
    • 
  
  • Be careful with the grid boundaries to avoid index out of range errors
    •

Steps to solve by this approach:

 Step 1: Check if the grid is valid. If it's null or empty, return 0.
 Step 2: Initialize a counter for the number of islands.
 Step 3: Iterate through each cell in the grid.
 Step 4: When we find a '1', increment the island counter.
 Step 5: Use DFS to mark all connected '1's as visited (by changing them to '0').
 Step 6: Continue iterating through the grid until all cells have been checked.
 Step 7: Return the final count of islands.

Submitted Code :