LeetCode752-打开轮盘锁

BFS

unordered_set:      insert   find     begin  end

queue   :      push   pop    front   last

 

 

 

 

 

 

class Solution {

public:

    string plusone(string str,int i){

        if(str[i]=='9'){

            str[i]='0';

        }

        else{

            str[i]=str[i]+1;

        }

        return str;

    }

    string downone(string str,int i){

        if(str[i]=='0'){

            str[i]='9';

        }

        else{

            str[i]=str[i]-1;

        }

        return str;

    }

 

    int openLock(vector<string>& deadends, string target) {

        unordered_set<string> deadset(deadends.begin(),deadends.end());

        queue<string> q;

        q.push("0000");

        unordered_set<string> visited;

        visited.insert("0000");

        int step=0;

        while(!q.empty()){

            int size=q.size();

            for(int i=0;i<size;i++){

                string str=q.front();

                q.pop();

                if(deadset.find(str)!=deadset.end()){

                    continue;

                }

                if(str==target){

                    return step;

                }

                for(int j=0;j<4;j++){

                    string up=plusone(str,j);

                    if(!visited.count(up)){

                        q.push(up);

                        visited.insert(up);

                    }

                    string down=downone(str,j);

                    if(!visited.count(down)){

                        q.push(down);

                        visited.insert(down);

                    }

                }

            }

            step++;

        }

        return -1;

    }

};

/*

http://www.cplusplus.com/reference/unordered_set/unordered_set/

*/