leetcode--Number of Islands

最新推荐文章于 2020-04-18 21:21:46 发布

crazy__chen

最新推荐文章于 2020-04-18 21:21:46 发布

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本文介绍了一种计算二维网格中岛屿数量的方法。通过遍历每个单元格，并使用广度优先搜索来标记相连的陆地，以此统计独立岛屿的数量。示例包括了具体的实现代码。

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Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

Example 1:

Answer: 1

Example 2:

Answer: 3

public class Solution {
    public int numIslands(char[][] grid) {
        int res = 0;
        int rows = grid.length;
        if(rows==0) return res;
		int cols = grid[0].length;
		if(cols==0) return res;
		int[] xdir = new int[]{1,-1,0,0};
		int[] ydir = new int[]{0,0,1,-1};
		ArrayList<Integer> queue_x = new ArrayList<Integer>();
		ArrayList<Integer> queue_y = new ArrayList<Integer>();
		
		for(int i=0;i<rows;i++){
			for(int j=0;j<cols;j++){
				if(grid[i][j]=='1'){
					res++;
					queue_x.add(i);queue_y.add(j);
					int low = 0;
					int high = 1;
					while(low<high){
						for(int k=0;k<4;k++){
							int x = queue_x.get(low)+xdir[k];
							int y = queue_y.get(low)+ydir[k];
							if(x>=0&&x<rows&&y>=0&&y<cols){
								if(grid[x][y]=='1'){
									grid[x][y]='0';
									queue_x.add(x);
									queue_y.add(y);
									high++;
								}
							}
						}
						low++;
					}
					queue_x.clear();queue_y.clear();
				}
			}
		}
		return res;
    }
}