22.Generate Parentheses
发布时间:2020-12-16 18:13:17 所属栏目:大数据 来源:网络整理
导读:Given n pairs of parentheses,write a function to generate all combinations of well-formed parentheses. For example,given n = 3,a solution set is: [ “((()))”,“(()())”,“(())()”,“()(())”,“()()()” ] java解法: public class Solution {
Given n pairs of parentheses,write a function to generate all combinations of well-formed parentheses. For example,given n = 3,a solution set is:
java解法: public class Solution {
public static void main(String[] args) {
new Solution().generateParenthesis(3);
}
public List<String> generateParenthesis(int n) {
backtrack(new ArrayList<String>(),"",0,n);
List<String> res = new ArrayList<String>();
backtrackOptmise(res,new char[2*n],n,0);
return res;
}
private void backtrackOptmise(ArrayList<String> strings,char[] cur,int n,int idx,int left,int right) {//通过使用char[], index的方式来优化运行速度
if (idx == n * 2) {
strings.add(new String(cur));
return;
}
if (left < n) {
cur[idx] = '(';
backtrackOptmise(strings,cur,idx + 1,left + 1,right);
}
if (right < left) {
cur[idx] = ')';
backtrackOptmise(strings,left,right + 1);
}
}
private List<String> backtrack(List<String> list,String str,int right,int max) {
if (left < max) {
backtrack(list,str + "(",right,max);
}
if (right < left) {
backtrack(list,str + ")",right + 1,max);
}
if (str.length() == max * 2) {
list.add(str);
}
return list;
}
}
golang: func generateParenthesis(n int) []string {
var strs []string
backtrack(&strs,n)
return strs
}
func backtrack(strs *[]string,str string,right,max int ){
if len(str) == max *2 {
*strs = append(*strs,str)
return
}
if left < max {
backtrack(strs,max)
}
if right < left {
backtrack(strs,str+ ")",right + 1,max)
}
}
相同道理,这里也可以通过byte数组进行优化; func generateParenthesis(n int) []string {
var strs []string
var gen func(left,right int,buff []byte)
gen = func(left,buff []byte) {
if left + right == n *2 {
strs = append(strs,string(buff))
return
}
if left < n {
gen(left + 1,append(buff,'('))
}
if right < left {
gen(left,right + 1,')'))
}
}
gen(0, 0,make([]byte,0, 2*n))
return strs
}
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