Ok, here's the problem that I have: using C# I want to format a string by printing out a certain number of characters, then skipping a certain number of characters and then again print, skip.
For example: I want to print 3 characters by skipping the next 2.
So this:
ABCDEFGHIJKL
would become this:
ABCFGHKL
I have only made that it could skip every 2,3,4 and so on characters and I couldn't think of how to approach this further.
Here is so far what I have
string text;
int print = 3;
int skip = 2;
StreamReader file = new StreamReader(#"c:\test.txt");
while ((text = file.Readtext()) != null)
{
string[] stringArray = new string[text.Length];
char ch;
for (int i = 0; i < text.Length; i++)
{
ch = text[i];
stringArray[i] = ch.ToString();
}
for (int i = 0; i < stringArray.Length; i+=skip)
{
Console.Write(stringArray[i]);
}
}
Thanks.
Thank you guys for various great solutions, I really appreciate your help! Thanks!
int take = 3;
int skip = 2;
string s = "ABCDEFGHIJKL";
var newstr = String.Join("", s.Where((c,i) => i % (skip + take) < take));
EDIT
Here are my test results....
int take = 3;
int skip = 2;
string s = String.Join("",Enumerable.Repeat("0123456789", 200));
var t1 = Measure(10000, () => { var newstr = String.Join("", s.Where((c, i) => i % (skip + take) < take)); });
var t2 = Measure(10000, () => { var newstr = new string(s.Where((c, i) => i % (skip + take) < take).ToArray()); });
var t3 = Measure(10000, () => { var newstr = GetString(s, take, skip); });
long Measure(int n,Action action)
{
action(); //JIT???
var sw = Stopwatch.StartNew();
for (int i = 0; i < n; i++)
{
action();
}
return sw.ElapsedMilliseconds;
}
OUTPUT:
1665 ms. (String.Join)
1154 ms. (new string())
7457 ms. (Sayse's GetString)
EDIT 2
Modifying Sayse's answer as below gives the fastest result among the codes i tested. (311 ms)
public string GetString(string s, int substringLen, int skipCount)
{
StringBuilder newString = new StringBuilder(s.Length);
for (int i = 0; i < s.Length; i += skipCount)
{
for (int j = 0; j < substringLen && i < s.Length; j++)
{
newString.Append(s[i++]);
}
}
return newString.ToString();
}
I like I4V's answer more but heres one way to achieve this
public string GetString(string s, int substringLen, int skipCount)
{
string newString = "";
for (int i = 0; i < s.Length; i += skipCount)
{
for (int j = 0; j < substringLen && i < s.Length; j++)
{
newString += s[i++];
}
}
return newString;
}
Edit Benchmark stated my way was faster
var newStr2 = new Program().GetString(a, take, skip);
var newstr = String.Join("", a.Where((c, i) => i % (skip + take) < take));
sw.Start();
for (int i = 0; i < 1000000; i++)
{
newStr2 = new Program().GetString(a, take, skip);
}
sw.Stop();
Console.WriteLine("my way: " + sw.Elapsed.ToString());
sw.Reset();
sw.Start();
for (int i = 0; i < 1000000; i++)
{
newstr = String.Join("", a.Where((c, iv) => iv % (skip + take) < take));
}
sw.Stop();
Console.WriteLine("I4V way: " + sw.Elapsed.ToString());
Output
my way: 00:00:00.7634927
I4V way: 00:00:01.0183307
int print = 3;
int skip = 2;
Boolean isPrintState = true;
int statePosition = 0;
StringBuilder Sb = new StringBuilder();
using (TextReader reader = new StreamReader(#"c:\test.txt")) {
while (true) {
int Ch = reader.Read();
if (Ch < 0)
break;
statePosition += 1;
if ((isPrintState && (statePosition > print)) || (!isPrintState && (statePosition > skip))) {
statePosition = 1;
isPrintState = !isPrintState;
}
if (isPrintState)
Sb.Append((Char) Ch);
}
}
Console.Write(Sb.ToString());
Amidst so many good looking answer, mine might not be so sophisticated but I thought I would post it anyways. Simple logic.
var take = 3;
var skip = 2;
StringBuilder source = new StringBuilder("ABCDEFGHIJKL");
StringBuilder result = new StringBuilder();
while (source.Length > 0)
{
if (source.Length >= take)
{
result.Append(source.ToString().Substring(0, take));
}
else
{
result.Append(source.ToString());
}
if (source.Length > skip + take)
{
source.Remove(0, skip + take);
}
else
source.Clear();
}
This how to do that.
I think this may be more clear if you are not familiar with Lambda expression
int print = 3;
int skip = 2;
string str = "ABCDEFGHILKL";
StringBuilder stringBuilder = new StringBuilder();
string res = String.Empty;
int i = 0;
while (i < str.Length)
{
stringBuilder.Append(str.Substring(i, Math.Min(print, str.Length - i)));
i += print + skip;
}
Console.WriteLine(stringBuilder.ToString());
Related
I have a StringBuilder result and I want to reverse it but in C# the StringBuilder doesn't support .Reverse() so first I cast it to a string and then I reverse it and add a "$" to the end of string.
but the answer is like this:
System.Linq.Enumerable+<ReverseIterator>d__75`1[System.Char]" string
how can I fix this?
StringBuilder result = new StringBuilder();
List<string> matrix = new List<string>();
List<int> indexes = new List<int>();
for (int i = 0; i < bwt.Length; i++)
{
matrix.Add("" + bwt[i]);
indexes.Add(i);
}
indexes.Sort((o1, o2) => matrix[o1].CompareTo(matrix[o2]));
int current = indexes[0];
for (int i = 0; i < bwt.Length - 1; i++)
{
int index = indexes.IndexOf(current);
string next = bwt[index].ToString();
result.Append(next);
current = index;
}
// return result.ToString().ToString() + "$";
StringBuilder allows you to access and manipulate the characters through their indexes.
string stringToReverse = "abcdefghijk";
var sb = new StringBuilder(stringToReverse);
for (int i = 0, j = sb.Length - 1; i < sb.Length / 2; i++, j--) {
char temp = sb[i];
sb[i] = sb[j];
sb[j] = temp;
}
string reversed = sb.ToString();
But I made a Test which shows that #Mendhak's version is faster. One million repetitions with strings of length 100
StringBuilder: 974 ms
Mendhak: 209 ms
So on my PC it takes just 209 ns to reverse the string with Mendhak's solution. Just because a solution looks faster it must not be faster. Array.Reverse calls the external method private static extern bool TrySZReverse(Array array, int index, int count); which is highly optimized.
The test:
static class ReverseString
{
const string stringToReverse = "abcdex.dfkjvhw4o5i8yd,vfjhe4iotuwyflkcjadhrlniqeuyfmln mclf8yuertoicer,tpoirsd,kfngoiw5r8t7ndlrgjhfg";
public static string TestStringBuilder()
{
var sb = new StringBuilder(stringToReverse);
for (int i = 0, j = sb.Length - 1; i < sb.Length / 2; i++, j--) {
char temp = sb[i];
sb[i] = sb[j];
sb[j] = temp;
}
return sb.ToString();
}
// By Mendhak
public static string TestArrayReverse()
{
char[] arr = stringToReverse.ToString().ToCharArray();
Array.Reverse(arr);
return new string(arr);
}
public static void Compare()
{
string result1 = TestStringBuilder();
string result2 = TestArrayReverse();
Console.WriteLine($"Are result1 and 2 equal? {result1 == result2}");
Measure("StringBuilder", TestStringBuilder);
Measure("Array.Reverse", TestArrayReverse);
Console.ReadKey();
}
public static void Measure(string method, Func<string> sut)
{
const int NTests = 1000000;
var stopWatch = new Stopwatch();
stopWatch.Start();
for (int i = 0; i < NTests; i++) {
sut();
}
stopWatch.Stop();
Console.WriteLine($"{method} = {stopWatch.ElapsedMilliseconds} ms");
}
}
You will need to take a few extra steps to reverse your string. Build it as you normally would in your stringbuilder (result), then
char[] arr = result.ToString().ToCharArray();
Array.Reverse(arr);
return new string(arr) + "$";
I am trying to optimize my code, I want to call Parallel.For inside a Parallel.ForEach(). I am not sure how can I do so. If I do see that the results are not correct. My code reverses the word within a sentence.
changed that for loop and it works.
for (int i = word.Length - 1; i >= 0; i--)
Here is my original code which fails.
public string Test()
{
string s = "Hello how are you";
if (s.Length > 0)
{
StringBuilder reverseS = new StringBuilder(s.Length);
string[] words = s.Split(' ');
Parallel.ForEach(words, word =>
{
StringBuilder builder = new StringBuilder(word.Length);
Parallel.For(0, word.Length - 1, i =>
//for (int i = word.Length - 1; i >= 0; i--)
{
builder.Append(word[i]);
});
reverseS.Append(builder);
reverseS.Append(" ");
});
return reverseS.ToString();
}
else
{
return "";
}
}
olleH woh era uoy
I see you have to reverse the chars but keep word positions. I don't know how good is the code below in comparison to your solution, so you can have some performance tests.
The idea is to reverse the words in array in the main thread and start a parallel one if we encounter a very long word.
private void Reverse()
{
const int extremelyLongWordLength = 100000;
var tasks = new List<Task>();
var wordStart = 0;
var arr = "Hello how are you".ToCharArray();
for (var i = 0; i < arr.Length; i++)
{
if (arr[i] == ' ')
{
var wordEnd = i - 1;
if (wordEnd - wordStart >= extremelyLongWordLength)
{
tasks.Add(ReverseWordAsTask(arr, wordStart, wordEnd));
}
else
{
ReverseWord(arr, wordStart, wordEnd);
}
wordStart = i + 1;
}
}
if (wordStart != arr.Length - 1)
{
if (arr.Length - 1 - wordStart > extremelyLongWordLength)
{
tasks.Add(ReverseWordAsTask(arr, wordStart, arr.Length - 1));
}
else
{
ReverseWord(arr, wordStart, arr.Length - 1);
}
}
Task.WaitAll(tasks.ToArray());
var modifiedString = new string(arr);
}
private static Task ReverseWordAsTask(char[] arr, int start, int end)
{
return Task.Run(() =>
{
var halfWordIndex = start + (end - start) / 2;
for (var i = start; i < halfWordIndex; i++)
{
var temp = arr[i];
var opposite = end - (i - start);
arr[i] = arr[opposite];
arr[opposite] = temp;
}
});
}
private static void ReverseWord(char[] arr, int start, int end)
{
var halfWordIndex = start + (end - start) / 2;
for (var i = start; i < halfWordIndex; i++)
{
var temp = arr[i];
var opposite = end - (i - start);
arr[i] = arr[opposite];
arr[opposite] = temp;
}
}
I am trying to solve this question:
Write a function that finds the zero-based index of the longest run in a string. A run is a consecutive sequence of the same character. If there is more than one run with the same length, return the index of the first one.
For example, IndexOfLongestRun("abbcccddddcccbba") should return 6 as the longest run is dddd and it first appears on index 6.
Following what i have done:
private static int IndexOfLongestRun(string str)
{
char[] array1 = str.ToCharArray();
//Array.Sort(array1);
Comparer comparer = new Comparer();
int counter =1;
int maxCount = 0;
int idenxOf = 0;
for (int i =0; i<array1.Length-1 ; i++)
{
if (comparer.Compare(array1[i],array1[i+1]) == 0)
{
counter++;
}
else {
if(maxCount < counter)
{
maxCount = counter;
idenxOf = i - counter + 1;
}
counter = 1;
}
}
return idenxOf ;
}
}
public class Comparer : IComparer<char>
{
public int Compare(char firstChar, char nextChar)
{
return firstChar.CompareTo(nextChar);
}
}
The problem is that when i get to the last index for example "abbccaaaaaaaaaa"
which is a in this case, and when i=14 (taking this string as example) and when i<array1.Length-1 statment is false, the for loop jumps directrly to return indexOf; and return the wrong index, I am trying to find out how to push the forloop to continue the implementation so idenxOf could be changed to the right index. Any help please?
You could check whether a new best score is achieved for each iteration when current == previous. Minimally slower, but it allows you to write shorter code by omitting an extra check after the loop:
int IndexOfLongestRun(string input)
{
int bestIndex = 0, bestScore = 0, currIndex = 0;
for (var i = 0; i < input.Length; ++i)
{
if (input[i] == input[currIndex])
{
if (bestScore < i - currIndex)
{
bestIndex = currIndex;
bestScore = i - currIndex;
}
}
else
{
currIndex = i;
}
}
return bestIndex;
}
Promote the loop variable i to method scope and repeat the conditional block if (maxCount < counter) { ... } right after the loop exit. Thus, it executes one more time after the loop completes
private static int IndexOfLongestRun(string str)
{
char[] array1 = str.ToCharArray();
//Array.Sort(array1);
Comparer comparer = new Comparer();
int counter = 1;
int maxCount = 0;
int idenxOf = 0;
int i;
for (i = 0; i < array1.Length - 1; i++)
{
if (comparer.Compare(array1[i], array1[i + 1]) == 0)
{
counter++;
}
else
{
if (maxCount < counter)
{
maxCount = counter;
idenxOf = i - counter + 1;
}
counter = 1;
}
}
if (maxCount < counter)
{
maxCount = counter;
idenxOf = i - counter + 1;
}
return idenxOf;
}
As usual late, but joining the party. A natural classic algorithm:
static int IndexOfLongestRun(string input)
{
int longestRunStart = -1, longestRunLength = 0;
for (int i = 0; i < input.Length; )
{
var runValue = input[i];
int runStart = i;
while (++i < input.Length && input[i] == runValue) { }
int runLength = i - runStart;
if (longestRunLength < runLength)
{
longestRunStart = runStart;
longestRunLength = runLength;
}
}
return longestRunStart;
}
At the end you have both longest run index and length.
public static int IndexOfLongestRun(string str)
{
var longestRunCount = 1;
var longestRunIndex = 0;
var isNew = false;
var dic = new Dictionary<int, int>();
for (var i = 0; i < str.Length - 1; i++)
{
if (str[i] == str[i + 1])
{
if (isNew) longestRunIndex = i;
longestRunCount++;
isNew = false;
}
else
{
isNew = true;
dic.Add(longestRunIndex, longestRunCount);
longestRunIndex = 0;
longestRunCount = 1;
}
}
return dic.OrderByDescending(x => x.Value).First().Key;
}
This will return -1 if the string is empty and you have the flexibility of returning the index and the count depending on your specification.
string myStr = "aaaabbbbccccccccccccdeeeeeeeee";
var longestIndexStart = -1;
var longestCount = 0;
var currentCount = 1;
var currentIndexStart = 0;
for (var idx = 1; idx < myStr.Length; idx++)
{
if (myStr[idx] == myStr[currentIndexStart])
currentCount++;
else
{
if (currentCount > longestCount)
{
longestIndexStart = currentIndexStart;
longestCount = currentCount;
}
currentIndexStart = idx;
currentCount = 1;
}
}
return longestIndexStart;
The accepted answer from Kvam works great for small strings, but as the length approaches 100,000 characters (and perhaps this isn't needed), its efficiency wains.
public static int IndexOfLongestRun(string str)
{
Dictionary<string, int> letterCount = new Dictionary<string, int>();
for (int i = 0; i < str.Length; i++)
{
string c = str.Substring(i, 1);
if (letterCount.ContainsKey(c))
letterCount[c]++;
else
letterCount.Add(c, 1);
}
return letterCount.Values.Max();
}
This solution is twice as fast as Kvam's with large strings. There are, perhaps, other optimizations.
I have gone through my code and tried to make it as efficient as i can think possible. Still i can not get this program to run all the way through without freezing my box. The maximum amount of time that i have let it run without it freezing it was about 2 hours. I can not believe this did not execute in that amount of time.
Is it an issue with my computer or is this brute force method of solving this problem that inefficient.
What are some ways that i can avoid this type of inefficiency when writing methods in the future?
private void Form1_Load(object sender, EventArgs e)
{
ArrayList listOfAbundantNumbers = new ArrayList();
ArrayList listOfSums = new ArrayList();
long total = 0;
for (int i = 1; i < 20162; i++)
{
if (isAbundandt(i))
{
listOfAbundantNumbers.Add(i);
}
total+=i;
}
for (int i = 1; i < listOfAbundantNumbers.Count; i++)
{
for (int a = 0; a < listOfAbundantNumbers.Count; a++)
{
long temp1 = Convert.ToInt64(listOfAbundantNumbers[i]);
long temp2 = Convert.ToInt64(listOfAbundantNumbers[a]);
long num = temp1 + temp2;
if(listOfSums.Contains(num) == false)
{
listOfSums.Add(num);
}
}
}
for (int i = 1; i < listOfAbundantNumbers.Count; i++)
{
long temp1 = Convert.ToInt64(listOfAbundantNumbers[i]);
total -= temp1;
}
printLn(total + "");
}
private ArrayList divisorList(long input)
{
ArrayList divisors = new ArrayList();
for (long i = 2; i < Math.Round(Math.Sqrt(input),0,0); i++)
{
long temp = input % i;
if (temp == 0)
{
divisors.Add(i);
divisors.Add(input / i);
}
}
return divisors;
}
private Boolean isAbundandt(long input)
{
long sum = 0;
ArrayList divisor = divisorList(input);
for (int i = 0; i < divisor.Count; i++)
{
long temp1 = Convert.ToInt64(divisor[i]);
sum += temp1;
}
sum++;
if (sum > input)
{
return true;
}
return false;
}
Avoid using ArrayList, prefer generic collection such as List<Int64> because you conversion may be quite expensive.
There is a part in your program which is in O(n^3). It can be reduce to O(n^2) easily. Just replace the following code (O(n) because of List<T>.Contains):
if(listOfSums.Contains(num) == false)
{
listOfSums.Add(num);
}
by:
listOfSums.Add(num);
where listOfSums is now a HashSet<Int64> (it's used to have a collection without duplicates).
Moreover, you can reduce the time for populating the listOfSums by a factor of 2 by just noticing that if you exchange i and a, the sum is the same, then, only one of the two combinations is added to the listOfSums.
You can replace:
for (int i = 1; i < listOfAbundantNumbers.Count; i++)
for (int a = 0; a < listOfAbundantNumbers.Count; a++)
by;
for (int i = 1; i < listOfAbundantNumbers.Count; i++)
for (int a = 0; a <= i; a++)
The final code is:
private static void Main()
{
List<Int64> listOfAbundantNumbers = new List<Int64>();
HashSet<Int64> listOfSums = new HashSet<Int64>();
long total = 0;
for (int i = 1; i < 20162; i++)
{
if (isAbundandt(i))
{
listOfAbundantNumbers.Add(i);
}
total += i;
}
for (int i = 0; i < listOfAbundantNumbers.Count; i++)
for (int a = 0; a <= i; a++)
{
long temp1 = Convert.ToInt64(listOfAbundantNumbers[i]);
long temp2 = Convert.ToInt64(listOfAbundantNumbers[a]);
long num = temp1 + temp2;
listOfSums.Add(num);
}
for (int i = 1; i < listOfAbundantNumbers.Count; i++)
{
long temp1 = Convert.ToInt64(listOfAbundantNumbers[i]);
total -= temp1;
}
Console.WriteLine(total + "");
}
private static List<Int64> divisorList(long input)
{
List<Int64> divisors = new List<Int64>();
for (long i = 2; i < Math.Round(Math.Sqrt(input), 0, 0); i++)
{
long temp = input % i;
if (temp == 0)
{
divisors.Add(i);
divisors.Add(input / i);
}
}
return divisors;
}
private static Boolean isAbundandt(long input)
{
long sum = 0;
List<Int64> divisor = divisorList(input);
for (int i = 0; i < divisor.Count; i++)
{
long temp1 = divisor[i];
sum += temp1;
}
sum++;
if (sum > input)
{
return true;
}
return false;
}
I need a method that returns every other character in a string starting with the first character. For example, a method call with ("Java-language") returns "Jv-agae."
private static void NewMethod(string word)
{
// here comes the code
}
var str = "Java-language";
var xx = new string(str.Where((ch, index) => index % 2 == 0).ToArray());
Console.WriteLine(xx);
Or this one:
var xx = string.Join<char>("", str.Where((ch, index) => (index & 1) == 0));
probably little different then everybody else: :-)
protected static IEnumerable<char> EverySecondChar(string word)
{
for(int i = 0; i < word.Length; i += 2)
yield return word[i];
}
string result = new string(EverySecondChar("Java-language").ToArray());
Here is my suggestion for you:
private string TakeEverySecondChar(string input)
{
var result = string.Empty;
for (int i = 0; i < input.Length; i+=2)
{
result += input.Substring(i, 1);
}
return result;
}
Console.Clear();
string Lang = "Java-language";
string[] LangArr = new string[Lang.Length];
char LangChar;
for (int i = 0; i < Lang.Length; i++)
{
LangChar = Lang[i];
LangArr[i] = LangChar.ToString();
}
for (int i = 0; i < LangArr.Length; i++)
{
Console.Write(LangArr[i]);
i++;
}
Console.ReadLine();
public String strip2ndchar(string text)
{
string final="";
int i = 0;
foreach (char a in text.ToCharArray())
{
if (i % 2 == 0)
final += a;
i++;
}
return final;
}