C# 随机拆分字符串

Question

I have a string like this:

string str = "ABCDEFGHI"

I want a result like:

string str1 = "AB";
string str2 = "CDEF";
string str3 = "G";
string str4 = "HI";

The idea is to randomly partitioning a string into a sequence of substring with random length.

I've tried the following:

public static string SplitString(string input)
    {
        string result = "";
        int j = 0;
        for (int i = 0; i < input.Length; i++)
        {
            Random random = new Random();
            j = random.Next(i+1, input.Length);
            string subString = input.Substring(i,j); //ERROR
            i = j-1;
            Console.WriteLine("New substring: " + subString);
            result = result + subString;
        }
        return result;
    }

It looks like this approach is not correct at all, because when I create a substring and the i index is greater than the j , the program goes in exception.

Is there a way to avoid this error?

Answer 1

Substring(Int32, Int32) extracts a substring of length j starting from index i, which will break once i+j >= input.Length - i is true.

Example: Substring(2,2) applied to "ABCDEF" should return "CD". In your specific case it would be possible to have something like Substring(4,5) throwing an Exception since the String does not have enough elements. At some point this loop will always cause an exception.

More details on the use of Substring can be found here: https://learn.microsoft.com/en-us/do.net/api/system.string.substring?view.netcore-3.1

Some things you can fix:

• Generate a random number in 1 to input.Length - i instead of 1 to input.Length
• Set i = i + j - 1 instead of i = j - 1

Algorithm:

1. Step

• i = 0
• Randomly roll j in 0 to (input.Length-1)
• Output j first letters starting from index i.
• Set i = i + j - 1

2. Step

• i = j
• Randomly roll j in 0 to (input.Length-1 - i)
• Output j first letters starting from index i.
• Set i = i + j - 1

3. Continue