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);
}
}
}