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695. Max Area of Island 👍

  • Time: $O(mn)$
  • Space: $O(1)$
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class Solution {
 public:
  int maxAreaOfIsland(vector<vector<int>>& grid) {
    int ans = 0;

    for (int i = 0; i < grid.size(); ++i)
      for (int j = 0; j < grid[0].size(); ++j)
        ans = max(ans, dfs(grid, i, j));

    return ans;
  }

 private:
  int dfs(vector<vector<int>>& grid, int i, int j) {
    if (i < 0 || i == grid.size() || j < 0 || j == grid[0].size())
      return 0;
    if (grid[i][j] != 1)
      return 0;

    grid[i][j] = 2;

    return 1 +                                          //
           dfs(grid, i + 1, j) + dfs(grid, i - 1, j) +  //
           dfs(grid, i, j + 1) + dfs(grid, i, j - 1);
  }
};

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class Solution {
  public int maxAreaOfIsland(int[][] grid) {
    int ans = 0;

    for (int i = 0; i < grid.length; ++i)
      for (int j = 0; j < grid[0].length; ++j)
        ans = Math.max(ans, dfs(grid, i, j));

    return ans;
  }

  private int dfs(int[][] grid, int i, int j) {
    if (i < 0 || i == grid.length || j < 0 || j == grid[0].length)
      return 0;
    if (grid[i][j] != 1)
      return 0;

    grid[i][j] = 2;

    return 1 +                                      //
        dfs(grid, i + 1, j) + dfs(grid, i - 1, j) + //
        dfs(grid, i, j + 1) + dfs(grid, i, j - 1);
  }
}

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class Solution:
  def maxAreaOfIsland(self, grid: list[list[int]]) -> int:
    def dfs(i: int, j: int) -> int:
      if i < 0 or i == len(grid) or j < 0 or j == len(grid[0]):
        return 0
      if grid[i][j] != 1:
        return 0

      grid[i][j] = 2

      return 1 + dfs(i + 1, j) + dfs(i - 1, j) + dfs(i, j + 1) + dfs(i, j - 1)

    return max(dfs(i, j) for i in range(len(grid)) for j in range(len(grid[0])))