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Java-based LeetCode algorithm problem solutions, regularly updated

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package g0001_0100.s0022_generate_parentheses;

// #Medium #Top_100_Liked_Questions #Top_Interview_Questions #String #Dynamic_Programming
// #Backtracking #Algorithm_II_Day_11_Recursion_Backtracking #Udemy_Backtracking/Recursion
// #Big_O_Time_O(2^n)_Space_O(n) #2023_08_09_Time_0_ms_(100.00%)_Space_41.7_MB_(97.17%)

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

/**
 * 22 - Generate Parentheses\.
 *
 * Medium
 *
 * Given `n` pairs of parentheses, write a function to _generate all combinations of well-formed parentheses_.
 *
 * **Example 1:**
 *
 * **Input:** n = 3
 *
 * **Output:** ["((()))","(()())","(())()","()(())","()()()"] 
 *
 * **Example 2:**
 *
 * **Input:** n = 1
 *
 * **Output:** ["()"] 
 *
 * **Constraints:**
 *
 * *   `1 <= n <= 8`
**/
public class Solution {
    public List generateParenthesis(int n) {
        StringBuilder sb = new StringBuilder();
        List ans = new ArrayList<>();
        return generate(sb, ans, n, n);
    }

    private List generate(StringBuilder sb, List str, int open, int close) {
        if (open == 0 && close == 0) {
            str.add(sb.toString());
            return str;
        }
        if (open > 0) {
            sb.append('(');
            generate(sb, str, open - 1, close);
            sb.deleteCharAt(sb.length() - 1);
        }
        if (close > 0 && open < close) {
            sb.append(')');
            generate(sb, str, open, close - 1);
            sb.deleteCharAt(sb.length() - 1);
        }
        return str;
    }
}