leetcode Add to List 200. Number of Islands

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:

11110
11010
11000
00000

Answer: 1

Example 2:

11000
11000
00100
00011

Answer: 3

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AC代码

public class Solution {    public void dfs(int x,int y,char [][] grid){        if(x<0||x>=grid.length||y<0||y>=grid[0].length||grid[x][y]!='1'){            return ;        }        grid[x][y]=0;        dfs(x-1,y,grid);        dfs(x,y-1,grid);        dfs(x+1,y,grid);        dfs(x,y+1,grid);    }    public int numIslands(char[][] grid) {        int answer=0;        for(int i=0;i<grid.length;i++){            for(int j=0;j<grid[i].length;j++){                if(grid[i][j]=='1'){                    dfs(i,j,grid);                    answer++;                }            }        }        return answer;    }}

bfs  

AC代码

public class Solution {    static int dx[]={-1,1,0,0};static int dy[]={0,0,-1,1};class Node{int x;int y;}    public void bfs(int x,int y,char [][] a){        Queue<Node> queue=new LinkedList<Node>();Solution leet=new Solution();Node node=leet.new Node();a[x][y]=0;node.x=x;node.y=y;queue.offer(node);while(queue.size()!=0){Node node1=queue.poll();for(int i=0;i<4;i++){int xx=node1.x+dx[i];int yy=node1.y+dy[i];if(xx>=0&&xx<a.length&&yy>=0&&yy<a[x].length&&a[xx][yy]=='1'){a[xx][yy]='0';Node node2=leet.new Node();node2.x=xx;node2.y=yy;queue.offer(node2);}}}    }    public int numIslands(char[][] grid) {        int answer=0;        for(int i=0;i<grid.length;i++){            for(int j=0;j<grid[i].length;j++){                if(grid[i][j]=='1'){                    bfs(i,j,grid);                    answer++;                }            }        }        return answer;    }}