Max Area of Island: the idea to remember.

The core insight

Flood fill each unvisited land cell, count its component, and retain the largest area.

Why it works

Each land cell belongs to exactly one connected component and contributes once when marked on discovery.

The mistake to avoid

Use four directions, not diagonals. This implementation marks the input grid as visited.

Commented Java solution

Use java.util.* imports and a surrounding solution class. Tree snippets assume the standard TreeNode definition; linked lists use ListNode and Clone Graph uses a Node with val and neighbors; Copy Random List uses Node with val, next and random. Read the input assumptions above.

// Java reference adapted from neetcode-gh/leetcode (MIT).
// Flood fill each unvisited land cell, count its component, and retain the largest area.
int maxArea = 0;

public int maxAreaOfIsland(int[][] grid) {
    maxArea = 0; // Reset per call; component searches mutate the grid.
  for (int i = 0; i < grid.length; i++) {
    for (int j = 0; j < grid[0].length; j++) {
      maxArea = Math.max(maxArea, 
                  maxAreaOfIsland(grid, i, j));
    }
  }

  return maxArea;
}

public int maxAreaOfIsland(int[][] grid, int r, int c) {
  if (r < 0 || c < 0 || 
      r == grid.length || 
      c == grid[0].length || 
      grid[r][c] == 0) {
        return 0;  
  }

  grid[r][c] = 0;

  return (1 + maxAreaOfIsland(grid, r + 1, c) +
              maxAreaOfIsland(grid, r - 1, c) +
              maxAreaOfIsland(grid, r, c + 1) +
              maxAreaOfIsland(grid, r, c - 1));
}

Java reference adapted from neetcode-gh/leetcode · MIT license

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