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22. Generate Parentheses

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:

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

难度：medium

题目：给定n对圆括号，写函数产生其所有格式良好的组合形式。

思路：右边括号数一定不能大于左边，然后利用递归来实现。

Runtime: 1 ms, faster than 100.00% of Java online submissions for Generate Parentheses.

Memory Usage: 27.8 MB, less than 7.34% of Java online submissions for Generate Parentheses.

class Solution {
    public List<String> generateParenthesis(int n) {
        List<String> result = new ArrayList<>();
        generateParenthesis(0, 0, n, new StringBuilder(), result);
        return result;
    }
    
    private void generateParenthesis(int left, int right, int n, StringBuilder sb, List<String> result) {
        if (left < right) {
            return;
        }
        if (left == right && n == left) {
            result.add(sb.toString());
            return;
        }
        
        if (left < n && left >= right) {
            sb.append("(");
            generateParenthesis(left + 1, right, n, sb, result);
            sb.deleteCharAt(sb.length() - 1);
        }
        
        if (right < left) {
            sb.append(")");
            generateParenthesis(left, right + 1, n, sb, result);
            sb.deleteCharAt(sb.length() - 1);
        }
    }
}

原文 https://segmentfault.com/a/1190000018116657

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