LeetCode: 733. Flood Fill

题目： 733. Flood Fill(https://leetcode.com/problems/flood-fill/description/)

解法1：

将符合条件的坐标放在一个队列里面，每次取一个（取完就在队列中移除），然后检查该坐标上下左右四个点中符合要求的坐标放进队列里，直到队列为空为止。

class Solution {
   public int[][] floodFill(int[][] image, int sr, int sc, int newColor) {
		Queue<Location> queue = new LinkedList<>();

		Location start = new Location(sr, sc);
		queue.offer(start);
		int old = image[sr][sc];

       if(newColor == old) {
			return image;
		}
       
		int rowLen = image.length;
		int colLen = image[0].length;

		while (!queue.isEmpty()) {
			Location curr = queue.poll();
			int currRow = curr.getRow();
			int currCol = curr.getColumn();
			image[currRow][currCol] = newColor;

			Location up = new Location(currRow + 1, currCol);
			Location down = new Location(currRow - 1, currCol);
			Location left = new Location(currRow, currCol - 1);
			Location right = new Location(currRow, currCol + 1);
			if (currRow + 1 < rowLen && image[up.getRow()][up.getColumn()] == old) {
				queue.offer(up);
			}
			if (currRow - 1 >= 0 && image[down.getRow()][down.getColumn()] == old) {
				queue.offer(down);
			}
			if (currCol - 1 >= 0 && image[left.getRow()][left.getColumn()] == old) {
				queue.offer(left);
			}
			if (currCol + 1 < colLen && image[right.getRow()][right.getColumn()] == old) {
				queue.offer(right);
			}
		}
		return image;
	}

	public static class Location {
		private int row;
		private int column;

		public Location(int row, int column) {
			this.row = row;
			this.column = column;
		}

		public int getRow() {
			return row;
		}

		public void setRow(int row) {
			this.row = row;
		}

		public int getColumn() {
			return column;
		}

		public void setColumn(int column) {
			this.column = column;
		}

		@Override
		public boolean equals(Object o) {
			if (this == o) {
				return true;
			}
			if (o == null || getClass() != o.getClass()) {
				return false;
			}
			Location location = (Location) o;
			return row == location.row && column == location.column;
		}

		@Override
		public int hashCode() {
			return Objects.hash(row, column);
		}
	}
}

解法2:

使用Java的ForkJoinPool， 对于每个符合条件的点生成一个RecursiveAction，然后再在这个点的上下左右生成符合条件点的RecursiveAction。

class Solution {
   public int[][] floodFill(int[][] image, int sr, int sc, int newColor) {
		ForkJoinPool pool = new ForkJoinPool();
		RecursiveAction action = new FillAction(new Location(sr, sc), newColor, image);
		pool.submit(action);
		action.join();
		pool.shutdown();
		return image;
	}

	public static class Location {
		private int row;
		private int column;

		public Location(int row, int column) {
			this.row = row;
			this.column = column;
		}

		public int getRow() {
			return row;
		}

		public void setRow(int row) {
			this.row = row;
		}

		public int getColumn() {
			return column;
		}

		public void setColumn(int column) {
			this.column = column;
		}

		@Override
		public String toString() {
			return "Location [row=" + row + ", column=" + column + "]";
		}

	}

	public static class FillAction extends RecursiveAction {
		private Location location;
		private int newColor;
		private volatile int[][] image;

		public FillAction(Location location, int newColor, int[][] image) {
			this.location = location;
			this.newColor = newColor;
			this.image = image;
		}

		@Override
		protected void compute() {

			int rowLen = image.length;
			int colLen = image[0].length;

			int currRow = location.getRow();
			int currCol = location.getColumn();
			int old = image[currRow][currCol];
			if (newColor == old) {
				return;
			}
			image[currRow][currCol] = newColor;

			Location up = new Location(currRow + 1, currCol);
			Location down = new Location(currRow - 1, currCol);
			Location left = new Location(currRow, currCol - 1);
			Location right = new Location(currRow, currCol + 1);

			List<RecursiveAction> actions = new ArrayList<>();
			if (currRow + 1 < rowLen && image[up.getRow()][up.getColumn()] == old) {
				RecursiveAction action = new FillAction(up, newColor, image);
				action.fork();
				actions.add(action);
			}
			if (currRow - 1 >= 0 && image[down.getRow()][down.getColumn()] == old) {
				RecursiveAction action = new FillAction(down, newColor, image);
				action.fork();
				actions.add(action);
			}
			if (currCol - 1 >= 0 && image[left.getRow()][left.getColumn()] == old) {
				RecursiveAction action = new FillAction(left, newColor, image);
				action.fork();
				actions.add(action);
			}
			if (currCol + 1 < colLen && image[right.getRow()][right.getColumn()] == old) {
				RecursiveAction action = new FillAction(right, newColor, image);
				action.fork();
				actions.add(action);
			}
			
			for(RecursiveAction action: actions) {
				action.join();
			}
		}
	}
}