[LeetCode] Number of Islands-优快云博客

本文介绍了一种利用深度优先搜索算法计算二维网格地图中岛屿数量的方法。通过遍历地图并标记已访问的陆地，算法准确计算出岛屿总数。

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

解题思路

深度优先搜索，要求的结果就是图中连通分量的个数。更详细的思路可以参考Find the number of islands。

实现代码

//Runtime:13ms
class Solution {
public:
    int numIslands(vector<vector<char>> &grid) {
        if (grid.empty() || grid[0].empty()) return 0;
        int row = grid.size();
        int col = grid[0].size();
        int cnt = 0;
        for (int i = 0; i < row; i++)
        {
            for (int j = 0; j < col; j++)
            {
                if (grid[i][j] == '1')
                {
                    cnt++;
                    dfs(grid, i, j);
                }
            }
        }

        return cnt;
    }

private:
    void dfs(vector<vector<char>> &grid, int row, int col)
    {
        if (row < 0 || row >= grid.size() || col < 0 || col >= grid[0].size() || grid[row][col] != '1')
        {
            return;
        }

        grid[row][col] = 'X';
        dfs(grid, row, col + 1);
        dfs(grid, row + 1, col);
        dfs(grid, row, col - 1);
        dfs(grid, row - 1, col);
    }
};