Posts Tagged 【dfs】Number of Islands

最新推荐文章于 2024-11-01 09:00:00 发布

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本文介绍如何使用深度优先搜索（DFS）算法解决岛屿数量计算问题，通过遍历二维网格，统计由陆地（'1'）组成的岛屿数量，岛屿被水（'0'）包围且可通过上下左右连接。

Number of Islands

Total Accepted: 5548 Total Submissions: 26482 My Submissions

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

Credits:
Special thanks to @mithmatt for adding this problem and creating all test cases.

//如果是弄个visited[][]就是stack over flow，直接将grid[i][j]='0'
public class Solution {
    public int numIslands(char[][] grid) {
        if(grid == null || grid.length == 0) return 0;
        int count = 0;
        for(int i = 0;i<grid.length;i++) 
            for(int j = 0;j<grid[0].length;j++) {
                if(grid[i][j] == '1') {
                    count++;
                    dfs(grid,i,j);
                }
            }
        return count;
    }
    private void dfs(char[][] grid,int i,int j) {
        if(i <0 || i>=grid.length || j <0 || j>=grid[0].length || grid[i][j] == '0')
            return;
        grid[i][j] = '0';
        dfs(grid,i-1,j);
        dfs(grid,i+1,j);
        dfs(grid,i,j-1);
        dfs(grid,i,j+1);
    }
}

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