Search a 2D Matrix

Medium 30 pts New · no attempts yet csharp

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Search a 2D Matrix — Persistent Systems interview prep · Binary Search

Classic interview problem #74.

Input (stdin)

Line 1: rows\nNext rows\nLast line: target

Output (stdout)

true or false

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

Examples

Sample

Input

3
1 3 5 7
10 11 16 20
23 30 34 60
3

Output

true

Static hints

Input format: Line 1: rows\nNext rows\nLast line: target
DSA Interview 150 — Binary Search
Problem #74
Frequently asked at Persistent Systems
Binary Search

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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: rows\nNext rows\nLast line: target

}
}

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

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()
    {
int m = int.Parse(Console.ReadLine());
var mat = new int[m][];
for (int i = 0; i < m; i++) mat[i] = Ria();
int target = int.Parse(Console.ReadLine());
int lo = 0, hi = m * mat[0].Length - 1;
bool found = false;
while (lo <= hi) {
    int mid = lo + (hi - lo) / 2;
    int val = mat[mid / mat[0].Length][mid % mat[0].Length];
    if (val == target) { found = true; break; }
    if (val < target) lo = mid + 1; else hi = mid - 1;
}
Wb(found);
    }
}

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Explanation

Step 1 / 1

Persistent Systems interview context: Search a 2D Matrix is a Medium Binary Search problem — Binary search on index or on the answer (binary search on value).

Use the animation above to step through each move before writing code.

Pattern: Binary Search

Read from stdin, write to stdout. Classic interview problem #74.

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