Shifting a String in C#

Question

  static void Main(string[] args)
  {
     string s = "ABCDEFGH";
     string newS = ShiftString(s);
     Console.WriteLine(newS);
  }
  public static string ShiftString(string t)
  {
     char[] c = t.ToCharArray();
     char save = c[0];
     for (int i = 0; i < c.Length; i++)
     {
        if (c[i] != c[0])
        c[i] = c[i - 1];
     }
     Console.WriteLine(c);
     String s = new string(c);
     return s;
  }

I need to shift the string s one space to the left, so i end up with the string: "BCDEFGHA" So i thought about changing the string into a char array and work my way from there, but im not sure how to succesfully make this work. I'm pretty certain i need a for loop, but i need some help on how to shift the char sequence one space to the left.

You said you end up with "BCDEFGHA". Isn't that what you expect? What result do you expect when given the input "ABCDEFGH" ? — zs2020, Feb 24 '13 at 16:08
Sorry, i may have phared it incorrectly. I am expecting the result "BCDEFGHA", but it is not what my current output is. — user2104751, Feb 24 '13 at 16:18

score 16 · Accepted Answer · answered Feb 24 '13 at 15:52

16

how about this?

public static string ShiftString(string t)
{
    return t.Substring(1, t.Length - 1) + t.Substring(0, 1); 
}

answered Feb 24 '13 at 15:52

John Woo

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Thanks, that seemed to work, but i'm not 100% sure how this actually works. Would be kind to explain why it does? – user2104751 Feb 24 '13 at 16:21
Imagine you have this string `ABC`. this part `t.Substring(1, t.Length - 1)` will yield `BC` while this one `t.Substring(0, 1)` will return `A`. – John Woo Feb 24 '13 at 16:23
2

Oh wait, i may know. The t.Substring(1, t.Length - 1) translated to "BCDEFGH" and t.Substring(0, 1) translated to "A", and by concatenating these we get "BCDEFGHA"? – user2104751 Feb 24 '13 at 16:24

Alina B. · Answer 2 · 2013-02-24T16:04:19.667

12

You can try this:

s = s.Remove(0, 1) + s.Substring(0, 1);

As an extension method:

public static class MyExtensions
{
    public static string Shift(this string s, int count)
    {
        return s.Remove(0, count) + s.Substring(0, count);
    }
}

Then you can use:

s = s.Shift(1);

edited Feb 24 '13 at 16:04

answered Feb 24 '13 at 15:54

Alina B.

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8
18

score 9 · Answer 3 · answered Feb 24 '13 at 16:29

The algorithm to solve this type of problem about shift n positions is duplicate the string, concatenate together and get the substring. ( n < length(string) )

string s = "ABCDEFGH";
string ss = s + s; // "ABCDEFGHABCDEFGH"

if you want to shift n position, you can do

var result = ss.Substring(n, s.length);

SunsetQuest · Answer 4 · 2020-09-21T03:11:45.480

5

In C# 8 and above...

Rotate Right by one...

t = myString[^1] + myString[..^1];

Or, Rotate Left by one...

t = myString[1..] + myString[0];

Or, Rotate Right by an amount...

t = myString[^amount..] + myString[..^amount];

Or, Rotate Left by an amount...

t = myString[amount..] + myString[..amount];

edited Sep 21 '20 at 03:11

answered Jan 09 '20 at 00:26

SunsetQuest

8,041
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score 3 · Answer 5 · answered Feb 24 '13 at 15:54

3

Personally I'd do this:

public static string ShiftString(string t){
    string firstLetter = t.Substring(0, 1);

    return t.Substring(1) + firstLetter;
}

answered Feb 24 '13 at 15:54

Grant Clements

984
6
14

sorry can't +1 you for that because that answer was already used. – Samuel Allan Apr 07 '14 at 14:42

score 2 · Answer 6 · answered Feb 24 '13 at 15:58

2

You can take advantage of the fact that string is IEnumerable<char>:

public static string ShiftString(string t){
    return new String(t.Skip(1).Concat(t).Take(t.Length).ToArray());
}

answered Feb 24 '13 at 15:58

driis

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score 2 · Answer 7 · answered Sep 21 '20 at 09:20

Using Span<T> we can significantly improve the performance. E.g.:

public static class StringExtensions
{
    public static string ShiftString(this string s)
    {
        return string.Concat(s.AsSpan(1), s.AsSpan(0, 1));
    }
}

Benchmark

This answer + existing answers. Using spans, the shifting of the string becomes both faster and produces less garbage.

|  Method |     Data |     Mean |   Median | Allocated |
|-------- |--------- |---------:|---------:|----------:|
|    L33t | ABCDEFGH | 18.56 ns | 18.21 ns |      40 B |
|  Zs2020 | ABCDEFGH | 36.04 ns | 35.20 ns |      96 B |
| JohnWoo | ABCDEFGH | 47.69 ns | 47.39 ns |     104 B |
|  AlinaB | ABCDEFGH | 52.56 ns | 52.07 ns |     104 B |

Full test code

using System;
using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Configs;
using BenchmarkDotNet.Diagnosers;
using BenchmarkDotNet.Diagnostics.Windows;
using BenchmarkDotNet.Running;

namespace ConsoleApp10
{
    class Program
    {
        static void Main(string[] args)
        {
            var summary = BenchmarkRunner.Run<StringShiftTest>();
        }
    }

    [Config(typeof(Config))]
    public class StringShiftTest
    {
        private class Config : ManualConfig
        {
            public Config() => AddDiagnoser(MemoryDiagnoser.Default, new EtwProfiler());
        }

        [Params("ABCDEFGH")]
        public string Data;

        [Benchmark]
        public string L33t() => string.Concat(Data.AsSpan(1), Data.AsSpan(0, 1));

        [Benchmark]
        public string Zs2020() => (Data + Data).Substring(1, Data.Length);

        [Benchmark]
        public string JohnWoo() => Data.Substring(1, Data.Length - 1) + Data.Substring(0, 1);

        [Benchmark]
        public string AlinaB() => Data.Remove(0, 1) + Data.Substring(0, 1);
    }
}

Maksym Anurin · Answer 8 · 2013-02-24T16:07:35.563

1

The StringBuilder class give you better performance

static string ShiftString(string str)
{
    if (str == null) throw new ArgumentNullException();
    int strLen = str.Length;
    if (strLen == 0) return string.Empty;
    StringBuilder sb = new StringBuilder(strLen);
    sb.Append(str, 1, strLen - 1);
    sb.Append(str[0]);
    return sb.ToString();
}

edited Feb 24 '13 at 16:07

answered Feb 24 '13 at 16:00

Maksym Anurin

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Gurunath Navale · Answer 9 · 2014-09-16T14:38:31.300

Below methods take the number n which tells how many times you want to shift/rotate the string. I have taken the MOD by length of string if the number is greater than the length of string.

public static void Rotate(ref string str, int n)
    {
        //if the rotation/shift number is less than or =0 throw exception
        if (n < 1)
            throw new Exception("Negative number for rotation"); 
        //if the String is less than 1 character no need to shift
        if (str.Length < 1) throw new Exception("0 length string");

        if (n > str.Length) // If number is greater than the length of the string then take MOD of the number
        {
            n = n % str.Length;
        }

        StringBuilder s1=new StringBuilder(str.Substring(n,(str.Length - n)));
        s1.Append(str.Substring(0,n));
        str=s1.ToString();


    }

///You can make a use of Skip and Take functions of the String operations

 public static void Rotate1(ref string str, int n)
    {
        if (n < 1)
            throw new Exception("Negative number for rotation"); ;
        if (str.Length < 1) throw new Exception("0 length string");

        if (n > str.Length)
        {
            n = n % str.Length;
        }

        str = String.Concat(str.Skip(n).Concat(str.Take(n)));

    }

score 1 · Answer 10 · answered May 07 '17 at 16:18

1

you also can achieve that with a simple LINQ statement:

Note: the same can be achieved with simple for and/or while loop

string a = "ABCDEFGH";  
a = new string(Enumerable.Range(0, a.Length).Select(i => (a[(i+1)%a.Length])).ToArray());

answered May 07 '17 at 16:18

H.G.Kh

11
1

score 1 · Answer 11 · answered Apr 14 '20 at 16:40

C# 8.0

private static string ShiftString(string t, int shift)
{
    if (shift < 0)//left
    {
        shift = -shift;
        return t[shift..] + t[..shift];
    }
    else//right
    {
        return t[(t.Length - shift)..] + t[..(t.Length - shift)];
    }
}

Shifting a String in C#

11 Answers11

Benchmark

Full test code