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0022-generate-parentheses.java

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package arrays;

import java.util.ArrayList;

import java.util.Iterator;

import java.util.List;

import java.util.Stack;

public class Solution {

public static void main(String[] args) {

Solution sol = new Solution();

sol.generateParenthesis(3);

}

Stack<Character> stack = new Stack<>();

List<String> res = new ArrayList<>();

public List<String> generateParenthesis(int n) {

backtrack(0, 0, n);

return res;

}

private void backtrack(int openN, int closedN, int n) {

if (openN == closedN && closedN == n) {

StringBuilder sb = new StringBuilder();

for (Character c: stack) {

sb.append(c);

}

res.add(sb.toString());

}

if (openN < n) {

stack.push('(');

backtrack(openN + 1, closedN, n);

stack.pop();

}

if (closedN < openN) {

stack.push(')');

backtrack(openN, closedN + 1, n);

stack.pop();

}

}

}