[leetcode] Generate Parentheses

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Generate Parentheses

class Solution {public:    vector<string> generateParenthesis(int n) {        vector<string> res;        if(n>0){            generate(n,"",0,0,res);        }        return res;    }    //采用递归树的思想，当左括号数大于右括号数时可以加左或者右括号，否则只能加左括号，当左括号数达到n时，剩下全部加右括号。    void generate(int n,string s,int lf,int rg,vector<string> &res){        if(lf==n){//only can add ')'            res.push_back(s.append(n-rg,')'));            return;        }        generate(n,s+'(',lf+1,rg,res);//add '('        if(lf>rg){            generate(n,s+')',lf,rg+1,res);//add ')'        }    }};

class Solution {public:    void help(int n,int x,int y,string now,vector<string> &answer){//dfs        if(y==n){            answer.push_back(now);            return;        }        if(x<n){            help(n,x+1,y,now+"(",answer);//加入左括号        }        if(x>y){            help(n,x,y+1,now+")",answer);//加入右括号        }    }    vector<string> generateParenthesis(int n) {        vector<string> answer;        help(n,0,0,"",answer);        return answer;    }};

struct node{    int x,y;    string now;};class Solution {public:    void help(int n,vector<string> &answer){//bfs       if(n==0){           answer.push_back("");           return;       }       node start,tmp;       start.x=start.y=0;       start.now="";              queue<node> q;       for(q.push(start);!q.empty();q.pop()){           tmp=q.front();           node other;           if(tmp.x<n){               other.x=tmp.x+1;               other.y=tmp.y;               other.now=tmp.now+"(";               q.push(other);           }           if(tmp.x>tmp.y){               other.x=tmp.x;               other.y=tmp.y+1;               other.now=tmp.now+")";               if(other.y==n){//组合成功                   answer.push_back(other.now);               }else{                   q.push(other);               }           }       }    }    vector<string> generateParenthesis(int n) {        vector<string> answer;        help(n,answer);        return answer;    }};

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