Find the Duplicate Number

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Zoho interview context: Find the Duplicate Number is a Medium Linked List problem — Fast/slow pointers or in-place reversal — draw pointers before coding.

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Pattern: Linked List

Read from stdin, write to stdout. Classic interview problem #287.

Problem

Find the Duplicate Number — Zoho interview prep · Linked List

Classic interview problem #287.

Input (stdin)

Line 1: n+1 integers in range 1..n

Output (stdout)

Duplicate number

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

Examples

Sample

Input

1 3 4 2 2

Output

Hints

Input format: Line 1: n+1 integers in range 1..n
DSA Interview 150 — Linked List
Problem #287
Frequently asked at Zoho
Linked List

Your 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()
    {
        // Read from stdin (see problem statement for format)
        // Line 1: n+1 integers in range 1..n

}
}

Ready — edit the code above and click Run or Submit.

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()
    {
var nums = Ria();
int slow = nums[0], fast = nums[0];
do { slow = nums[slow]; fast = nums[nums[fast]]; } while (slow != fast);
slow = nums[0];
while (slow != fast) { slow = nums[slow]; fast = nums[fast]; }
Wi(slow);
    }
}

Try solving on your own first, then reveal the official answer.

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