22 Generate Parentheses – Medium
Problem:
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:
"((()))", "(()())", "(())()", "()(())", "()()()"
Thoughts:
Key idea is that, if you still have left parantheses left, you have two choice : insert a parantheses or a right parenthesis. But the condition for inserting right parenthesis is that used left ones is more than used right ones.
Solutions:
public class Solution {
public List<String> generateParenthesis(int n) {
List<String> result = new LinkedList<String>();
process("", n, n, result);
return result;
}
private void process(String prefix, int left, int right, List<String> result) {
if (left == 0 && right == 0) {
result.add(prefix);
return;
}
if (left > 0) {
process(prefix + '(', left - 1, right, result);
}
if (left < right) {
process(prefix + ')', left, right - 1, result);
}
}
}