LeetCode 22. Generate Parentheses

Description

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

Example

For example, given n = 3, a solution set is:

[
  "((()))",
  "(()())",
  "(())()",
  "()(())",
  "()()()"
]

Code

• java

import java.util.LinkedList;
class Solution {
    List<String> result;
    public void dfs(int n, int cnt, String str) {
        if(str.length() == 2*n) {
            result.add(str);
            return ;
        }
        if(cnt < n) {
            dfs(n, cnt+1, str+"(");
        } 
        if(str.length() < 2*cnt) {
            dfs(n, cnt, str+")");
        }
    }
    public List<String> generateParenthesis(int n) {
        result = new LinkedList<>();
        if(n > 0) dfs(n, 0, "");
        return result;
    }
}

• python

class Solution:
    def generateParenthesis(self, n: int) -> List[str]:
        list = []
        def dfs(n, cnt, s):
            if len(s) == 2*n:
                list.append(s)
                return
            if cnt < n:
                dfs(n, cnt+1, s+"(")
            if len(s) < 2*cnt:
                dfs(n, cnt, s+")")
        if n > 0:
            dfs(n, 0, "")
        return list

• Others’ Solution
• python

class Solution(object):
    def generateParenthesis(self, n):
        def generate(p, left, right, parens=[]):
            if left:         generate(p + '(', left-1, right)
            if right > left: generate(p + ')', left, right-1)
            if not right:    parens += p,
            return parens
        return generate('', n, n)

Conclusion

• py的嵌套函数挺好用
• 大佬的py版本写的很简洁