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Leetcode022-generateParenthneses

Posted on Edited on In Views: Valine:
Solution Report of LeetCode Acceptted

Description

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:

Example

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

Solution

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class Solution {
    public List<String> generateParenthesis(int n) {
        List<String> res = new ArrayList<>();
        if (n == 0) return res;
        
        helper(n, res, 0, 0, "");
        return res;
    }
    
    private void helper(int n, List<String> res, int left, int right, String cur){
        if (left == n && right == n) {
            res.add(cur);
            return;
        }
        int maxLeft = n - left;
        if (maxLeft > 0){
            cur += "(";
            helper(n, res, left + 1, right, cur);
            if (cur.length() > 1) cur = cur.substring(0, cur.length() - 1);
            else cur = "";
        }
        
        int maxRight = left - right;
        if (maxRight > 0){
            cur += ")";
            helper(n, res, left, right + 1, cur);
            if (cur.length() > 1) cur = cur.substring(0, cur.length() - 1);
            else cur = "";
        }
    }
}