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leetcode_java/src/main/java/LeetCodeJava/BFS/SurroundedRegions.java
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| package LeetCodeJava.BFS; | ||
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| // https://leetcode.com/problems/surrounded-regions/ | ||
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| import java.util.ArrayList; | ||
| import java.util.LinkedList; | ||
| import java.util.List; | ||
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| public class SurroundedRegions { | ||
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| // TODO : fix below | ||
| // V0 | ||
| // int[][] points = new int[][]{}; | ||
| // public void solve(char[][] board) { | ||
| // | ||
| // if (board.length == 1 && board[0].length == 1){ | ||
| // return; | ||
| // } | ||
| // | ||
| // int len = board.length; | ||
| // int width = board[0].length; | ||
| // | ||
| // // dfs | ||
| // // make points to "X" | ||
| // List<List<Integer>> tmp_points = _collect(board, 0, 0, new ArrayList<>()); | ||
| // if (tmp_points != null && _is_border(tmp_points)){ | ||
| // flip(tmp_points, board); | ||
| // } | ||
| // return; | ||
| // } | ||
| // | ||
| // private List<List<Integer>> _collect(char[][] board, int x, int y, List<List<Integer>> points){ | ||
| // | ||
| // int len = board.length; | ||
| // int width = board[0].length; | ||
| // | ||
| // if (x < 0 || x >= width || y < 0 || y >= len || board[y][x] == 'X'){ | ||
| // return null; | ||
| // } | ||
| // | ||
| // if (board[y][x] == 'O'){ | ||
| // List<Integer> cur = new ArrayList<>(); | ||
| // cur.add(x); | ||
| // cur.add(y); | ||
| // points.add(cur); | ||
| // } | ||
| // | ||
| // _collect(board, x+1, y, points); | ||
| // _collect(board, x-1, y, points); | ||
| // _collect(board, x, y+1, points); | ||
| // _collect(board, x, y-1, points); | ||
| // | ||
| // return points; | ||
| // } | ||
| // | ||
| // private Boolean _is_border(List<List<Integer>> points){ | ||
| // for (List<Integer> x : points){ | ||
| // if (x.get(0) == 0 || x.get(1) == 0){ | ||
| // return false; | ||
| // } | ||
| // } | ||
| // return true; | ||
| // } | ||
| // | ||
| // private void flip(List<List<Integer>> points, char[][] board){ | ||
| // for (List<Integer> x : points){ | ||
| // board[x.get(0)][x.get(1)] = 'X'; | ||
| // } | ||
| // } | ||
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| // V1 | ||
| // IDEA : DFS | ||
| // https://leetcode.com/problems/surrounded-regions/editorial/ | ||
| protected Integer ROWS = 0; | ||
| protected Integer COLS = 0; | ||
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| public void solve_1(char[][] board) { | ||
| if (board == null || board.length == 0) { | ||
| return; | ||
| } | ||
| this.ROWS = board.length; | ||
| this.COLS = board[0].length; | ||
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| 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)); | ||
| } | ||
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| // Step 2). mark the escaped cells | ||
| for (Pair<Integer, Integer> pair : borders) { | ||
| this.DFS(board, pair.first, pair.second); | ||
| } | ||
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| // 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'; | ||
| } | ||
| } | ||
| } | ||
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| protected void DFS(char[][] board, int row, int col) { | ||
| if (board[row][col] != 'O') | ||
| return; | ||
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| board[row][col] = 'E'; | ||
| if (col < this.COLS - 1) | ||
| this.DFS(board, row, col + 1); | ||
| if (row < this.ROWS - 1) | ||
| this.DFS(board, row + 1, col); | ||
| if (col > 0) | ||
| this.DFS(board, row, col - 1); | ||
| if (row > 0) | ||
| this.DFS(board, row - 1, col); | ||
| } | ||
| } | ||
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| class Pair<U, V> { | ||
| public U first; | ||
| public V second; | ||
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| public Pair(U first, V second) { | ||
| this.first = first; | ||
| this.second = second; | ||
| } | ||
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| // V2 | ||
| // IDEA : BFS | ||
| // https://leetcode.com/problems/surrounded-regions/editorial/ | ||
| protected Integer ROWS = 0; | ||
| protected Integer COLS = 0; | ||
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| public void solve_2(char[][] board) { | ||
| if (board == null || board.length == 0) { | ||
| return; | ||
| } | ||
| this.ROWS = board.length; | ||
| this.COLS = board[0].length; | ||
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| 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)); | ||
| } | ||
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| // Step 2). mark the escaped cells | ||
| for (Pair<Integer, Integer> pair : borders) { | ||
| this.BFS(board, pair.first, pair.second); | ||
| } | ||
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| // 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'; | ||
| } | ||
| } | ||
| } | ||
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| protected void BFS(char[][] board, int r, int c) { | ||
| LinkedList<Pair2<Integer, Integer>> queue = new LinkedList<Pair2<Integer, Integer>>(); | ||
| queue.offer(new Pair2<>(r, c)); | ||
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| while (!queue.isEmpty()) { | ||
| Pair2<Integer, Integer> pair = queue.pollFirst(); | ||
| int row = pair.first, col = pair.second; | ||
| if (board[row][col] != 'O') | ||
| continue; | ||
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| board[row][col] = 'E'; | ||
| if (col < this.COLS - 1) | ||
| queue.offer(new Pair2<>(row, col + 1)); | ||
| if (row < this.ROWS - 1) | ||
| queue.offer(new Pair2<>(row + 1, col)); | ||
| if (col > 0) | ||
| queue.offer(new Pair2<>(row, col - 1)); | ||
| if (row > 0) | ||
| queue.offer(new Pair2<>(row - 1, col)); | ||
| } | ||
| } | ||
| } | ||
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| class Pair2<U, V> { | ||
| public U first; | ||
| public V second; | ||
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| public Pair2(U first, V second) { | ||
| this.first = first; | ||
| this.second = second; | ||
| } | ||
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| } |