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  • 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

     dfs

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

    bfs

    public class Solution {
        public int numIslands(char[][] grid) {
            int res = 0;
            Queue<int[]> queue = new LinkedList<>();
            for(int i = 0; i < grid.length; i++){
                for(int j = 0 ; j < grid[0].length; j++){
                    if(grid[i][j] == '1'){
                        res++;
                        queue.add(new int[]{i,j});
                        while(!queue.isEmpty()){
                            int point[] = queue.poll();
                            int row = point[0];
                            int col = point[1];
                            if(grid[row][col] == '0') continue;
                            grid[row][col] = '0';
                            if(row > 0)
                                queue.add(new int[]{row-1,col});
                            if(col > 0 )
                                queue.add(new int[]{row, col-1});
                            if(row < grid.length -1)
                                queue.add(new int[]{row+1, col});
                            if(col < grid[0].length -1)
                                queue.add(new int[]{row, col+1});
                        }
                    }
                }
            }
           
            return res;
        }
    }
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  • 原文地址:https://www.cnblogs.com/joannacode/p/5947915.html
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