-
Notifications
You must be signed in to change notification settings - Fork 0
/
RemoveIslands.java
68 lines (65 loc) · 1.93 KB
/
RemoveIslands.java
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
import java.util.*;
class Program {
// O(hw) time | O(hw) space
public int[][] removeIslands(int[][] matrix) {
// Write your code here.
int height = matrix.length;
int width = matrix[0].length;
boolean[][] onesConnectedToBorder = new boolean[height][width];
for (int c = 0; c < width; c++) {
markOnesConnectedToBorder(0, c, matrix, onesConnectedToBorder);
markOnesConnectedToBorder(height - 1, c, matrix, onesConnectedToBorder);
}
for (int r = 0; r < height; r++) {
markOnesConnectedToBorder(r, 0, matrix, onesConnectedToBorder);
markOnesConnectedToBorder(r, width - 1, matrix, onesConnectedToBorder);
}
for (int r = 0; r < height; r++) {
for (int c = 0; c < width; c++) {
if (onesConnectedToBorder[r][c]) {
continue;
}
matrix[r][c] = 0;
}
}
return matrix;
}
private static void markOnesConnectedToBorder(int row, int col, int[][] matrix, boolean[][] onesConnectedToBorder) {
if (matrix[row][col] != 1 || onesConnectedToBorder[row][col]) {
return;
}
Queue<int[]> queue = new LinkedList<>();
queue.add(new int[] { row, col });
while (!queue.isEmpty()) {
int[] position = queue.poll();
int r = position[0];
int c = position[1];
boolean alreadyVisited = onesConnectedToBorder[r][c];
if (alreadyVisited || matrix[r][c] != 1) {
continue;
}
onesConnectedToBorder[r][c] = true;
for (int[] neighbor : getNeighbors(r, c, matrix)) {
int nr = neighbor[0];
int nc = neighbor[1];
queue.add(new int[] { nr, nc });
}
}
}
private static List<int[]> getNeighbors(int row, int col, int[][] matrix) {
List<int[]> neighbors = new ArrayList<>();
if (row > 0) {
neighbors.add(new int[] { row - 1, col });
}
if (row < matrix.length - 1) {
neighbors.add(new int[] { row + 1, col });
}
if (col > 0) {
neighbors.add(new int[] { row, col - 1 });
}
if (col < matrix[0].length - 1) {
neighbors.add(new int[] { row, col + 1 });
}
return neighbors;
}
}