Skip to content

Latest commit

 

History

History
189 lines (131 loc) · 7.56 KB

explanation.md

File metadata and controls

189 lines (131 loc) · 7.56 KB
Raw

Minimum Days to Disconnect a Grid: Step-by-Step Explanation

This README provides a step-by-step explanation of how the C++, Java, JavaScript, and Python implementations of the "Minimum Days to Disconnect a Grid" problem work. Each explanation is broken down into logical steps without showing the actual code, allowing you to understand the thought process behind each solution.

C++ Code Explanation

1. Initial Check

  • Check if Grid is Already Disconnected:
    • Begin by checking if the grid is already disconnected, meaning there are separate landmasses. If so, return 0 days, as no action is needed.

2. Remove One Cell at a Time

  • Iterate Over the Grid:
    • Traverse each cell in the grid. If the cell contains land (1), temporarily change it to water (0).
  • Check for Disconnection:
    • After making the change, check if the grid has become disconnected. If it has, return 1 day, as only one removal is necessary.
  • Revert the Change:
    • If the grid remains connected, revert the cell back to land (1) and continue checking other cells.

3. Remove Two Cells at a Time

  • Nested Iteration:
    • If removing a single cell doesn’t work, try removing two cells. For each land cell, temporarily remove it and then try removing another land cell.
  • Check for Disconnection:
    • After each removal, check if the grid is disconnected. If it becomes disconnected, return 2 days.
  • Revert Both Changes:
    • If the grid remains connected, revert both cells back to land.

4. Return 2 Days by Default

  • Final Return:
    • If no disconnection occurs after trying to remove up to two cells, return 2 days as the grid can only be disconnected by removing at least two cells.

5. Helper Functions

  • Check Disconnection:
    • This function checks if the grid is disconnected by counting separate landmasses.
  • Breadth-First Search (BFS):
    • BFS is used to explore all connected land cells from a starting point.

Java Code Explanation

1. Initial Check

  • Check if Grid is Already Disconnected:
    • Begin by checking if the grid is already disconnected. If it is, return 0 days.

2. Remove One Land Cell

  • Iterate Over Each Cell:
    • Traverse each cell in the grid. If the cell is land (1), temporarily change it to water (0).
  • Check for Disconnection:
    • Check if the grid is now disconnected. If so, return 1 day.
  • Revert Change:
    • If the grid is still connected, revert the cell back to land.

3. Remove Two Land Cells

  • Try Removing Two Cells:
    • If removing a single cell doesn’t work, try removing two cells sequentially. For each land cell, temporarily change it to water, then try removing another cell.
  • Check for Disconnection:
    • After removing the second cell, check if the grid is disconnected. If it is, return 2 days.
  • Revert Changes:
    • If no disconnection occurs, revert both cells back to land.

4. Return 2 Days by Default

  • Final Return:
    • If no solution is found after trying to remove up to two cells, return 2 days as the default answer.

5. Helper Methods

  • Check Disconnection:
    • This method checks if the grid is disconnected by identifying separate landmasses.
  • Breadth-First Search (BFS):
    • BFS is used to explore all connected land cells, starting from a given cell.

JavaScript Code Explanation

1. Initial Check

  • Check for Initial Disconnection:
    • First, check if the grid is already disconnected. If so, return 0 days, as no changes are needed.

2. Remove One Land Cell

  • Iterate Through Each Cell:
    • Loop through each cell in the grid. If the cell is land (1), temporarily turn it into water (0).
  • Disconnection Check:
    • Check if the grid is disconnected after the change. If it is, return 1 day.
  • Revert Change:
    • If the grid remains connected, revert the cell back to land.

3. Remove Two Land Cells

  • Nested Loop for Two Removals:
    • If removing one cell doesn't work, attempt to remove two cells. For each land cell, temporarily turn it into water, and then try removing another land cell.
  • Check for Disconnection:
    • After both removals, check if the grid is disconnected. If it is, return 2 days.
  • Revert Both Changes:
    • If the grid is still connected, revert both cells back to land.

4. Return 2 Days by Default

  • Final Return:
    • If no solution is found after trying to remove up to two cells, return 2 days as the answer.

5. Helper Functions

  • Check Disconnection:
    • This function checks if the grid is disconnected by identifying separate landmasses.
  • Breadth-First Search (BFS):
    • BFS is used to explore all connected land cells, beginning from a starting cell.

Python Code Explanation

1. Initial Check

  • Check for Initial Disconnection:
    • Begin by checking if the grid is already disconnected. If it is, return 0 days.

2. Remove One Cell at a Time

  • Iterate Over the Grid:
    • Loop through each cell in the grid. If the cell contains land (1), temporarily turn it into water (0).
  • Check for Disconnection:
    • After the change, check if the grid has become disconnected. If it has, return 1 day.
  • Revert the Change:
    • If the grid remains connected, revert the cell back to land.

3. Remove Two Cells Sequentially

  • Nested Loop for Two Removals:
    • If removing one cell doesn't work, try removing two cells. For each land cell, temporarily remove it and then try removing another land cell.
  • Check for Disconnection:
    • After removing both cells, check if the grid is disconnected. If it is, return 2 days.
  • Revert Both Changes:
    • If the grid remains connected, revert both cells back to land.

4. Return 2 Days by Default

  • Final Return:
    • If no solution is found after trying to remove up to two cells, return 2 days.

5. Helper Functions

  • Check Disconnection:
    • This method checks if the grid is disconnected by counting separate landmasses.
  • Breadth-First Search (BFS):
    • BFS is used to explore all connected land cells, starting from the initial cell.

Go Code Explanation

  1. Define the Function Signature:

    • Start by defining the main function that takes an integer input representing the number of oranges.
    • The function returns the minimum number of days required to eat all the oranges.

  2. Base Case Check:

    • Implement a base case that immediately returns the number of days when the orange count is small (e.g., n <= 1). This handles the simplest scenarios without further computation.

  3. Memoization Setup:

    • Use a map or dictionary to store previously computed results for specific numbers of oranges. This helps in reducing redundant calculations by caching results.

  4. Recursive Calculation:

    • For the main logic, consider two primary cases:
      • Divisible by 2: Calculate the number of days required if the oranges are divisible by 2.
      • Divisible by 3: Similarly, calculate the days required if the oranges are divisible by 3.
    • In both cases, use the previously stored results in the map to avoid redundant calculations.

  5. Choose the Minimum Days:

    • From the possible scenarios, select the one that takes the minimum number of days.
    • Add 1 to account for the current day of the operation.

  6. Store the Result:

    • Store the result in the map for future reference, thus making the solution efficient.

  7. Return the Result:

    • Finally, return the minimum number of days required, as calculated.