Valid Parentheses

Easy 20 pts New · no attempts yet csharp

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Valid Parentheses — Cisco interview prep · Stack

Classic interview problem #20.

Input (stdin)

Line 1: bracket string

Output (stdout)

true or false

Your program must read from stdin and write the answer to stdout (no extra debug text).

Examples

Sample

Input

()[]{}

Output

true

Static hints

Input format: Line 1: bracket string
DSA Interview 150 — Stack
Problem #20
Frequently asked at Cisco
Stack

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Your solution

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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()
    {
        // Read from stdin (see problem statement for format)
        // Line 1: bracket string

}
}

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Official solution

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()
    {
string s = Console.ReadLine();
var st = new Stack<char>();
var pairs = new Dictionary<char, char> { [')']='(', [']']='[', ['}']='{' };
bool ok = true;
foreach (var ch in s) {
    if (ch == '(' || ch == '[' || ch == '{') st.Push(ch);
    else if (!st.Any() || st.Pop() != pairs[ch]) { ok = false; break; }
}
Wb(ok && st.Count == 0);
    }
}

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Explanation

Step 1 / 1

Cisco interview context: Valid Parentheses is a Easy 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 #20.

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