[email protected] [200] Number of Islands

https://leetcode.com/problems/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:

11110110101100000000

Answer: 1

Example 2:

11000110000010000011

Answer: 3

class Solution {
public:
    void dfs(vector<vector<char> >& grid, vector<vector<bool> >& vis, int x, int y) {
        int dir[4][2] = {{0,1}, {0,-1}, {1,0}, {-1,0}};

        for(int i=0;i<4;++i) {
            int nx = x + dir[i][0], ny = y + dir[i][1];
            if(nx<0 || ny<0 || nx>=grid.size() || ny>=grid[0].size() || vis[nx][ny] || grid[nx][ny] == ‘0‘) continue;
            vis[nx][ny] = true;
            dfs(grid, vis, nx, ny);
        }
    }
    int numIslands(vector<vector<char>>& grid) {
        if(grid.size() == 0) return 0;

        vector<vector<bool> > vis(grid.size(), vector<bool>(grid[0].size(), false));

        int res = 0;
        for(int i=0;i<grid.size();++i) {
            for(int j=0;j<grid[i].size();++j) {
                if(!vis[i][j] && grid[i][j] == ‘1‘) {
                    ++res;
                    dfs(grid, vis, i, j);
                }
            }
        }

        return res;
    }
};