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Leetcode200-numberOfIslands

Posted on Edited on In Views: Valine:
Solution Report of LeetCode Acceptted

Description

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

Example 1:

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Input:
11110
11010
11000
00000

Output: 1

Example 2:
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Input:
11000
11000
00100
00011

Output: 3

Solution

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class Solution {
    
    static int[][] dir = new int[][]{{1,0}, {-1, 0}, {0, 1}, {0, -1}};
    public int numIslands(char[][] grid) {
        int res = 0;
        if (grid == null || grid.length == 0 || grid[0].length == 0) return res;
        
        int m = grid.length;
        int n = grid[0].length;
        for (int i = 0; i < m; i++){
            for (int j = 0; j < n; j++){
                if (grid[i][j] == '1'){
                    res++;
                    clear(grid,i,j,m,n);
                }
            }
        }
        
        return res;
    }
    
    public void clear(char[][] grid, int x, int y, int m, int n){
        if (grid[x][y] == '0') return;
        
        grid[x][y] = '0';
        for (int i = 0; i < 4; i++){
            int nx = x + dir[i][0];
            int ny = y + dir[i][1];
            if (nx >=0 && nx < m && ny >= 0 && ny < n) clear(grid,nx,ny,m,n);
        }
    }
}