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| 20231006: quick_sort | ||
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| 20231002: 130 | ||
| 20231001: 417 | ||
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leetcode_java/src/main/java/LeetCodeJava/BFS/WallsAndGates.java
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| package LeetCodeJava.BFS; | ||
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| // https://leetcode.com/problems/walls-and-gates/description/ | ||
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| import java.util.*; | ||
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| public class WallsAndGates { | ||
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| // V0 | ||
| // IDEA : BFS | ||
| public void wallsAndGates(int[][] rooms) { | ||
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| class Pair<U, V, W> { | ||
| U key; | ||
| V value; | ||
| W value2; | ||
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| Pair(U key, V value, W value2) { | ||
| this.key = key; | ||
| this.value = value; | ||
| this.value2 = value2; | ||
| } | ||
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| U getKey() { | ||
| return this.key; | ||
| } | ||
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| V getValue() { | ||
| return this.value; | ||
| } | ||
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| W getValue2() { | ||
| return this.value2; | ||
| } | ||
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| } | ||
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| // edge case | ||
| if (rooms.length == 1 && rooms[0].length == 1) { | ||
| return; | ||
| } | ||
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| int space_cnt = 0; | ||
| int gete_cnt = 0; | ||
| int[][] dirs = {{1, 0}, {-1, 0}, {0, 1}, {0, -1}}; | ||
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| int len = rooms.length; | ||
| int width = rooms[0].length; | ||
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| // init queue | ||
| Queue<Pair> q = new LinkedList<Pair>(); | ||
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| // get cnt | ||
| for (int i = 0; i < width; i++) { | ||
| for (int j = 0; j < len; j++) { | ||
| if (rooms[j][i] == 0) { | ||
| gete_cnt += 1; | ||
| // NOTE !!! we should do BFS with "gete" instead of space point | ||
| q.add(new Pair(i, j, -1)); | ||
| } else if (rooms[j][i] == 2147483647) { | ||
| space_cnt += 1; | ||
| //q.add(new Pair(i, j, -1)); // append space point to queue, for BFS | ||
| } else { | ||
| //obstacle_cnt += 1; | ||
| } | ||
| } | ||
| } | ||
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| // if there is no gate or no space -> quit directly | ||
| if (gete_cnt == 0 || space_cnt == 0) { | ||
| return; | ||
| } | ||
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| // bfs | ||
| while (!q.isEmpty()) { | ||
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| Pair p = q.poll(); | ||
| int x = (int) p.getKey(); | ||
| int y = (int) p.getValue(); | ||
| int dist = (int) p.getValue2(); | ||
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| for (int[] dir : dirs) { | ||
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| int dx = dir[0]; | ||
| int dy = dir[1]; | ||
| int new_x = x + dx; | ||
| int new_y = y + dy; | ||
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| String idx = new_x + "-" + new_x; | ||
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| if (0 <= new_x && new_x < width && 0 <= new_x && new_y < len) { | ||
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| // NOTE !!! don't use logic in commented code | ||
| // if (rooms[new_y][new_x] == 0 && !seen.contains(idx)) { | ||
| // rooms[new_y][new_x] = dist; | ||
| // seen.add(idx); | ||
| // } else { | ||
| // dist += 1; | ||
| // q.add(new Pair(new_x, new_y, dist)); | ||
| // } | ||
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| // NOTE !!! we do NOTHING if point is out of border or point is "NOT a space" | ||
| if (new_x < 0 || new_x > width || new_y < 0 || new_y > len || rooms[new_y][new_x] != 2147483647) { | ||
| continue; | ||
| } | ||
| rooms[new_y][new_x] = rooms[y][x] + 1; | ||
| q.add(new Pair(new_x, new_y, dist + 1)); | ||
| } | ||
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| } | ||
| } | ||
| } | ||
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| // V1 | ||
| // IDEA BFS | ||
| // https://leetcode.com/problems/walls-and-gates/editorial/ | ||
| private static final int EMPTY = Integer.MAX_VALUE; | ||
| private static final int GATE = 0; | ||
| private static final List<int[]> DIRECTIONS = Arrays.asList( | ||
| new int[]{1, 0}, | ||
| new int[]{-1, 0}, | ||
| new int[]{0, 1}, | ||
| new int[]{0, -1} | ||
| ); | ||
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| public void wallsAndGates_1(int[][] rooms) { | ||
| int m = rooms.length; | ||
| if (m == 0) return; | ||
| int n = rooms[0].length; | ||
| Queue<int[]> q = new LinkedList<>(); | ||
| for (int row = 0; row < m; row++) { | ||
| for (int col = 0; col < n; col++) { | ||
| if (rooms[row][col] == GATE) { | ||
| q.add(new int[]{row, col}); | ||
| } | ||
| } | ||
| } | ||
| while (!q.isEmpty()) { | ||
| int[] point = q.poll(); | ||
| int row = point[0]; | ||
| int col = point[1]; | ||
| for (int[] direction : DIRECTIONS) { | ||
| int r = row + direction[0]; | ||
| int c = col + direction[1]; | ||
| if (r < 0 || c < 0 || r >= m || c >= n || rooms[r][c] != EMPTY) { | ||
| continue; | ||
| } | ||
| rooms[r][c] = rooms[row][col] + 1; | ||
| q.add(new int[]{r, c}); | ||
| } | ||
| } | ||
| } | ||
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| // V2 | ||
| // IDEA BRUTE FORCE (TLE) | ||
| // https://leetcode.com/problems/walls-and-gates/editorial/ | ||
| // private static final int EMPTY = Integer.MAX_VALUE; | ||
| // private static final int GATE = 0; | ||
| // private static final int WALL = -1; | ||
| // private static final List<int[]> DIRECTIONS = Arrays.asList( | ||
| // new int[] { 1, 0}, | ||
| // new int[] {-1, 0}, | ||
| // new int[] { 0, 1}, | ||
| // new int[] { 0, -1} | ||
| // ); | ||
| // | ||
| // public void wallsAndGates_2(int[][] rooms) { | ||
| // if (rooms.length == 0) return; | ||
| // for (int row = 0; row < rooms.length; row++) { | ||
| // for (int col = 0; col < rooms[0].length; col++) { | ||
| // if (rooms[row][col] == EMPTY) { | ||
| // rooms[row][col] = distanceToNearestGate(rooms, row, col); | ||
| // } | ||
| // } | ||
| // } | ||
| // } | ||
| // | ||
| // private int distanceToNearestGate(int[][] rooms, int startRow, int startCol) { | ||
| // int m = rooms.length; | ||
| // int n = rooms[0].length; | ||
| // int[][] distance = new int[m][n]; | ||
| // Queue<int[]> q = new LinkedList<>(); | ||
| // q.add(new int[] { startRow, startCol }); | ||
| // while (!q.isEmpty()) { | ||
| // int[] point = q.poll(); | ||
| // int row = point[0]; | ||
| // int col = point[1]; | ||
| // for (int[] direction : DIRECTIONS) { | ||
| // int r = row + direction[0]; | ||
| // int c = col + direction[1]; | ||
| // if (r < 0 || c < 0 || r >= m || c >= n || rooms[r][c] == WALL | ||
| // || distance[r][c] != 0) { | ||
| // continue; | ||
| // } | ||
| // distance[r][c] = distance[row][col] + 1; | ||
| // if (rooms[r][c] == GATE) { | ||
| // return distance[r][c]; | ||
| // } | ||
| // q.add(new int[] { r, c }); | ||
| // } | ||
| // } | ||
| // return Integer.MAX_VALUE; | ||
| // } | ||
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| } |
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