LeetCode 22 Generate Parentheses

连续两次随机到关于括号的题了，跟括号真有缘。。。

好了，别的不多说，上代码：

package ywheel.leetcode._22_generate_parentheses;

import java.util.ArrayList;
import java.util.List;

/**
* 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:
* "((()))", "(()())", "(())()", "()(())", "()()()"
*
* @author ywheel
*
*/
public class GenerateParentheses {
public List<String> generateParenthesis(int n) {
List<String> results = new ArrayList<String>();
if (n > 0) {
// the first one must be '('
generateNext(n, n - 1, "(", results);
}
return results;
}
private void generateNext(int n, int rest_num_left, String solution, List<String> results) {
if (rest_num_left > 0) {
// can append '('
generateNext(n, rest_num_left - 1, solution + "(", results);
if (solution.length() < (n - rest_num_left)*2) {
// can append ')'
generateNext(n, rest_num_left, solution + ")", results);
}
} else {
// has already append n '(', so the only
4000
one solution here
// is to append all the rest ')'
int rest_len = n*2 - solution.length();
while (rest_len > 0) {
solution += ")";
rest_len--;
}
results.add(solution);
}
}

public static void main(String[] args) {
GenerateParentheses solution = new GenerateParentheses();
List<String> result = solution.generateParenthesis(3);
if (result != null) {
for (String str : result) {
System.out.print(str + ",");
}
}
}
}