30 Day Challenge Day 18 | Leetcode 200. Number of Islands (BFS)

题解

Medium

用BFS再做了一遍。

class Solution {
public:
    int numIslands(vector<vector<char>>& grid) {
        if(grid.empty()) return 0;
        
        int count = 0;
        
        vector<vector<bool>> visited(grid.size(), vector<bool>(grid[0].size(), false));
        
        int dirs[4][2] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
        
        for(int i = 0; i < grid.size(); i++) {
            for(int j = 0; j < grid[0].size(); j++) {
                if(grid[i][j] == '0' || visited[i][j]) continue;
                
                count++;
                visited[i][j] = true;

                queue<vector<int>> q;
                q.push({i, j});
                
                while(!q.empty()) {
                    auto t = q.front();
                    q.pop();
                    
                    for(int k = 0; k < 4; k++) {
                        int x = t[0] + dirs[k][0];
                        int y = t[1] + dirs[k][1];
                        
                        if(x < 0 || x >= grid.size() || y < 0 || y >= grid[0].size())
                            continue;
                        
                        if(grid[x][y] == '1' && !visited[x][y]) {
                            visited[x][y] = true;
                            q.push({x, y});
                        }
                    }
                }
            }
        }
        
        return count;
    }
};