Step through the algorithm visually — use Play or the step buttons (inspired by AlgoMaster / visualgo).
PayPal interview context: Generate Parentheses is a Medium Stack problem — Monotonic stack or bracket matching — watch for O(n) single-pass solutions.
Use the animation above to step through each move before writing code.
Pattern: Stack
Read from stdin, write to stdout. Classic interview problem #22.
Generate Parentheses — PayPal interview prep · Stack
Classic interview problem #22.
Input (stdin)
Line 1: n pairs
Output (stdout)
Count of valid combinations (n=3 → 5)
Your program must read from stdin and write the answer to stdout (no extra debug text).
3
5
| Test | Status | Details |
|---|
Ready — edit the code above and click Run or Submit.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
class Program
{
static int[] Ria(string line = null)
{
line ??= Console.ReadLine();
if (string.IsNullOrWhiteSpace(line)) return Array.Empty<int>();
return line.Trim().Split(new[] { ' ', ',', '\t' }, StringSplitOptions.RemoveEmptyEntries)
.Select(int.Parse).ToArray();
}
static string[] Rsa()
{
int n = int.Parse(Console.ReadLine());
var arr = new string[n];
for (int i = 0; i < n; i++) arr[i] = Console.ReadLine();
return arr;
}
static void W(params object[] parts) => Console.WriteLine(string.Join(" ", parts));
static void Wb(bool v) => Console.WriteLine(v ? "true" : "false");
static void Wi(int v) => Console.WriteLine(v);
static void Ws(string v) => Console.WriteLine(v);
static void Main()
{
int n = int.Parse(Console.ReadLine());
var res = new List<string>();
void Dfs(int open, int close, StringBuilder sb) {
if (sb.Length == 2 * n) { res.Add(sb.ToString()); return; }
if (open < n) { sb.Append('('); Dfs(open + 1, close, sb); sb.Length--; }
if (close < open) { sb.Append(')'); Dfs(open, close + 1, sb); sb.Length--; }
}
Dfs(0, 0, new StringBuilder());
Wi(res.Count);
}
}Try solving on your own first, then reveal the official answer.