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LeetCode 1568: Minimum Number of Days to Disconnect Island Solution

Master LeetCode problem 1568 (Minimum Number of Days to Disconnect Island), a hard challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

1568. Minimum Number of Days to Disconnect Island

Hard
ArrayDepth-First SearchBreadth-First SearchMatrixStrongly Connected Component

Problem Explanation

Explanation:

To solve this problem, we can simulate disconnecting the island by converting each land cell to water one by one and checking if the grid becomes disconnected. We can use a depth-first search (DFS) to check if the grid is connected after each conversion. We need to consider two special cases - when the grid has only one island and when the grid is already disconnected.

  1. Count the number of islands in the initial grid.
  2. If there is only one island, return 0 because the grid is already disconnected.
  3. Iterate through each land cell in the grid.
  4. For each land cell, convert it to water and perform a DFS to check if the grid becomes disconnected.
  5. If the grid becomes disconnected, return the number of days it took to disconnect.
  6. If no disconnection occurs after trying all land cells, return 1 (at least 1 day is needed to disconnect).

Time complexity: O(m * n * m * n), where m is the number of rows and n is the number of columns in the grid. Space complexity: O(m * n) for the recursive DFS stack.

:

Solution Code

class Solution {
    public int minDays(int[][] grid) {
        int islands = countIslands(grid);
        if (islands != 1) {
            return 0;
        }
        
        int minDays = 2;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                if (grid[i][j] == 1) {
                    grid[i][j] = 0;
                    if (countIslands(grid) != 1) {
                        return 1;
                    }
                    grid[i][j] = 1;
                }
            }
        }
        
        return minDays;
    }
    
    private int countIslands(int[][] grid) {
        // Implement DFS to count the number of islands
    }
}

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