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update 130 java, add DataStructure/MyPair.java
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@yennanliu
yennanliu committed Oct 5, 2023
1 parent d5899dd commit 465cd10
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159 changes: 116 additions & 43 deletions leetcode_java/src/main/java/LeetCodeJava/BFS/SurroundedRegions.java
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Original file line number Diff line number Diff line change
Expand Up @@ -2,7 +2,6 @@

// https://leetcode.com/problems/surrounded-regions/

import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;

Expand Down Expand Up @@ -71,6 +70,17 @@ public class SurroundedRegions {
// V1
// IDEA : DFS
// https://leetcode.com/problems/surrounded-regions/editorial/

class Pair<U, V> {
public U first;
public V second;

public Pair(U first, V second) {
this.first = first;
this.second = second;
}
}

protected Integer ROWS = 0;
protected Integer COLS = 0;

Expand All @@ -83,6 +93,7 @@ public void solve_1(char[][] board) {

List<Pair<Integer, Integer>> borders = new LinkedList<Pair<Integer, Integer>>();
// Step 1). construct the list of border cells
// NOTE !!! this is "border" list for escaped celles (not considered as island)
for (int r = 0; r < this.ROWS; ++r) {
borders.add(new Pair(r, 0));
borders.add(new Pair(r, this.COLS - 1));
Expand All @@ -93,6 +104,8 @@ public void solve_1(char[][] board) {
}

// Step 2). mark the escaped cells
// NOTE !!! dfs only implement on "escaped cells"
// so
for (Pair<Integer, Integer> pair : borders) {
this.DFS(board, pair.first, pair.second);
}
Expand All @@ -109,10 +122,13 @@ public void solve_1(char[][] board) {
}

protected void DFS(char[][] board, int row, int col) {

if (board[row][col] != 'O')
return;

board[row][col] = 'E';

// TODO : double check below
if (col < this.COLS - 1)
this.DFS(board, row, col + 1);
if (row < this.ROWS - 1)
Expand All @@ -121,58 +137,59 @@ protected void DFS(char[][] board, int row, int col) {
this.DFS(board, row, col - 1);
if (row > 0)
this.DFS(board, row - 1, col);
}
}

class Pair<U, V> {

// V2
// IDEA : BFS
// https://leetcode.com/problems/surrounded-regions/editorial/
class Pair2<U, V> {
public U first;
public V second;

public Pair(U first, V second) {
public Pair2(U first, V second) {
this.first = first;
this.second = second;
}

}

// V2
// IDEA : BFS
// https://leetcode.com/problems/surrounded-regions/editorial/
protected Integer ROWS = 0;
protected Integer COLS = 0;
protected Integer ROWS2 = 0;
protected Integer COLS2 = 0;

public void solve_2(char[][] board) {
if (board == null || board.length == 0) {
return;
}
this.ROWS = board.length;
this.COLS = board[0].length;

List<Pair<Integer, Integer>> borders = new LinkedList<Pair<Integer, Integer>>();
// Step 1). construct the list of border cells
for (int r = 0; r < this.ROWS; ++r) {
borders.add(new Pair(r, 0));
borders.add(new Pair(r, this.COLS - 1));
}
for (int c = 0; c < this.COLS; ++c) {
borders.add(new Pair(0, c));
borders.add(new Pair(this.ROWS - 1, c));
}
if (board == null || board.length == 0) {
return;
}
this.ROWS2 = board.length;
this.COLS2 = board[0].length;

// Step 2). mark the escaped cells
for (Pair<Integer, Integer> pair : borders) {
this.BFS(board, pair.first, pair.second);
}
List<Pair<Integer, Integer>> borders = new LinkedList<Pair<Integer, Integer>>();
// Step 1). construct the list of border cells
for (int r = 0; r < this.ROWS2; ++r) {
borders.add(new Pair(r, 0));
borders.add(new Pair(r, this.COLS2 - 1));
}
for (int c = 0; c < this.COLS2; ++c) {
borders.add(new Pair(0, c));
borders.add(new Pair(this.ROWS2 - 1, c));
}

// Step 3). flip the cells to their correct final states
for (int r = 0; r < this.ROWS; ++r) {
for (int c = 0; c < this.COLS; ++c) {
if (board[r][c] == 'O')
board[r][c] = 'X';
if (board[r][c] == 'E')
board[r][c] = 'O';
}
// Step 2). mark the escaped cells
for (Pair<Integer, Integer> pair : borders) {
this.BFS(board, pair.first, pair.second);
}

// Step 3). flip the cells to their correct final states
for (int r = 0; r < this.ROWS2; ++r) {
for (int c = 0; c < this.COLS2; ++c) {
if (board[r][c] == 'O')
board[r][c] = 'X';
if (board[r][c] == 'E')
board[r][c] = 'O';
}
}
}

protected void BFS(char[][] board, int r, int c) {
LinkedList<Pair2<Integer, Integer>> queue = new LinkedList<Pair2<Integer, Integer>>();
Expand All @@ -195,16 +212,72 @@ protected void BFS(char[][] board, int r, int c) {
queue.offer(new Pair2<>(row - 1, col));
}
}

// V3
// IDEA : DFS
// https://leetcode.com/problems/surrounded-regions/solutions/3805983/java-100-faster-step-by-step-explained/
public void solve(char[][] board) {
int rows = board.length;
int cols = board[0].length;

int[] delRows = {-1, 0, 1, 0}; // Array to represent changes in row index to traverse in all four directions
int[] delCols = {0, 1, 0, -1}; // Array to represent changes in column index to traverse in all four directions

int[][] visited = new int[rows][cols]; // Matrix to keep track of visited cells

// Process first row and last row
for (int i = 0; i < cols; i++) {
// Process first row
if (board[0][i] == 'O' && visited[0][i] == 0) {
dfs(0, i, board, visited, delRows, delCols); // Call the dfs method to explore the connected region of 'O's
}
// Process last row
if (board[rows - 1][i] == 'O' && visited[rows - 1][i] == 0) {
dfs(rows - 1, i, board, visited, delRows, delCols); // Call the dfs method to explore the connected region of 'O's
}
}

// Process first and last column
for (int i = 0; i < rows; i++) {
// Process first column
if (board[i][0] == 'O' && visited[i][0] == 0) {
dfs(i, 0, board, visited, delRows, delCols); // Call the dfs method to explore the connected region of 'O's
}
// Process last column
if (board[i][cols - 1] == 'O' && visited[i][cols - 1] == 0) {
dfs(i, cols - 1, board, visited, delRows, delCols); // Call the dfs method to explore the connected region of 'O's
}
}

// Convert surrounded 'O's to 'X's
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
if (board[i][j] == 'O' && visited[i][j] == 0) {
board[i][j] = 'X'; // Mark the surrounded 'O's as 'X'
}
}
}
}

// Depth First Search (DFS) method to explore the connected region of 'O's
private static void dfs(int row, int col, char[][] board, int[][] visited, int[] delRows, int[] delCols) {
visited[row][col] = 1; // Mark the current cell as visited

class Pair2<U, V> {
public U first;
public V second;
int rows = board.length;
int cols = board[0].length;

public Pair2(U first, V second) {
this.first = first;
this.second = second;
// Explore all four directions
for (int i = 0; i < 4; i++) {
int newRow = row + delRows[i];
int newCol = col + delCols[i];

// Check if the new cell is within bounds and is an unvisited 'O'
if (newRow >= 0 && newRow < rows && newCol >= 0 && newCol < cols
&& board[newRow][newCol] == 'O' && visited[newRow][newCol] == 0) {
dfs(newRow, newCol, board, visited, delRows, delCols); // Recursively call dfs for the new cell
}
}
}

}

13 changes: 13 additions & 0 deletions leetcode_java/src/main/java/LeetCodeJava/DataStructure/MyPair.java
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Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
package LeetCodeJava.DataStructure;

public class MyPair<U, V> {

public U first;
public V second;

MyPair(U first, V second){
this.first = first;
this.second = second;
}

}

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