002 BFS 实现解开密码锁的最少次数 [C++]

// BFS
class Solution 
{
public:
    int openLock(vector<string>& deadends, string target) 
    {
        // BFS 模板,打印所有可能密码
        queue <string> q;
        unordered_set <string> version;
        unordered_set <string> dead;

        for (string str : deadends)  dead.insert(str);

        //把初始密码添加到队列中
        q.push("0000");
        version.insert("0000");

        int depth = 0;

        while (!q.empty())
        {
            int len = q.size();
            for (int i = 0; i < len; i++)
            {
                string cur = q.front();

                q.pop();            //使用队列中第一个元素后，立刻把其删除，不要放在后面删除，以防出现 bug

                //判断是否是正确密码
                if (dead.find(cur) != dead.end()) continue;
                if (cur == target) return depth;
                //if (!cur.compare(target)) return depth;

                for (int j = 0; j < 4; j++)
                {
                    //转动一次密码并添加到队列中
                    string up = plusone(cur, j);

                    //判断是否是回头路
                    if (version.find(up) == version.end())
                    {
                        q.push(up);
                        version.insert(up);
                    }
                    
                    string down = minnusone(cur, j);
                    if (version.find(down) == version.end())
                    {
                        q.push(down);
                        version.insert(down);
                    }
                }

                
            }
            depth++;
        }
        return -1;
    }

private:

    string plusone(string s, int i)
    {
        string ch = s;

        if (ch[i] == '9')   ch[i] = '0';
        else ch[i] += 1;
        return ch;
    }

    string minnusone(string s, int i)
    {
        string ch = s;

        if (ch[i] == '0')   ch[i] = '9';
        else ch[i] -= 1;
        return ch;
    }
};