LeetCode 200. Number of Islands--c++ dfs解法

LeetCode 200. Number of Islands

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LeetCode题解专栏：LeetCode题解
我做的所有的LeetCode的题目都放在这个专栏里，大部分题目Java和Python的解法都有。

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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:

Input:
11110
11010
11000
00000

Output: 1

Example 2:

Input:
11000
11000
00100
00011

Output: 3

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c++ dfs解法

class Solution {
public:
    int numIslands(vector<vector<char>>& grid)
    {
        int nr = grid.size();
           
        if(nr <= 0)
        {
            return 0;
        }
        int nc = grid[0].size();
    
        int num_islands = 0;
        for(int r = 0; r < nr; r++)
        {
            for(int c = 0; c < nc; c++)
            {
                if(grid[r][c] == '1')
                {
                    num_islands++;
                    dfs(grid,r,c);  
                }
            }
        }
        return num_islands;
    }
    
private:
    void dfs(vector<vector<char>>& grid, int r, int c)
    {
        int nr = grid.size();
        int nc = grid[0].size();
        
        grid[r][c] = '0';
        
        //Apply Depth first search coming from all directions
        if(r-1 >=0 && grid[r-1][c] == '1')
        {
            dfs(grid,r-1,c);
        }
        if(r+1 < nr && grid[r+1][c] == '1')
        {
            dfs(grid,r+1,c);
        }
        if(c-1 >= 0 && grid[r][c-1] == '1')
        {
            dfs(grid,r,c-1);
        }
        if(c+1 < nc && grid[r][c+1] == '1')
        {
            dfs(grid,r,c+1);
        }
    }
};