i have a problem with the code i showed below.
using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
namespace problem2
{
class Program
{
static void Main(string[] args)
{
int[] nums = Console.ReadLine().Split().Select(int.Parse).ToArray();
List<int> lst = nums.OfType<int>().ToList();
while (true)
{
string des = Console.ReadLine();
var output = Regex.Replace(des.Split(" ")[0], #"[^0-9a-zA-Z\ ]+", "");
if (output == "Add")
{
string val = Regex.Replace(des, "[^0-9]", "");
int value = int.Parse(val);
lst.Add(value);
}
else if(output == "Remove")
{
string val = Regex.Replace(des, "[^0-9]", "");
int value = int.Parse(val);
lst.Remove(value);
}else if(output == "Replace")
{
String result1 = System.Text.RegularExpressions.Regex.Match(des, #"\d+").Value;
var lastno = des.Split().Last();
List<int> lst2 = lst;
for (int i = 0; i < lst2.Count; i++)
{
if(lst[i] == int.Parse(result1))
{
lst[i] = int.Parse(lastno);
break;
}
}
lst = lst2;
}
else if(output == "Collapse")
{
string val = Regex.Replace(des, "[^0-9]", "");
int value = int.Parse(val);
for(int i = 0; i < lst.Count; i+=1)
{
int element = (int)lst[i];
if (element < value)
{
lst.RemoveAt(i);
}
else
{
continue;
}
}
}else if (output == "Mort")
{
PrintValues(lst);
break;
}
}
}
public static void PrintValues(IEnumerable myList)
{
foreach (Object obj in myList)
Console.Write("{0} ", obj);
Console.WriteLine();
}
}
}
more precisely with this part of the code:
else if(output == "Collapse")
{
string val = Regex.Replace(des, "[^0-9]", "");
int value = int.Parse(val);
for(int i = 0; i < lst.Count; i+=1)
{
int element = (int)lst[i];
if (element < value)
{
lst.RemoveAt(i);
}
else
{
continue;
}
}
I tried with all sorts of options but the loop misses elements. as an example
entrance:
1 2 -1 0 -3 9 8 7 2
Collapse 8
Mort
output:
9 8
but the program gives me this output:
2 0 9 8 2
I tried to see what the problem is through the debugger and there I found that the loop misses elements
It should be,
for(int i = 0; i < lst.Count; i+=1)
{
int element = (int)lst[i];
if (element < value)
{
lst.RemoveAt(i);
i--;
}
else
{
continue;
}
}
As #David784 mentioned at the comments. When you remove element the from the itterating collection. You miss 1 element everytime after you delete the i item.
To elaborate on #Berkay's comment: You're changing a list as you're looping through it. If i is 2 and you remove that element, then the element that used to be at index 3 now becomes 2, and so forth. His method of decrementing i will work. Another way would be to use a linq .Where statement instead:
var newList = lst.Where(e=> e>=value).ToList();
You are modifying the collection you are iterating through. This moves elements to other indexes and invalidates the i you determine for following elements in the for header. Better loop backwards
for (int i = lst.Count - 1; i >= 0; i--) {
// Now you can safely remove (or add) elements without affecting
// the index of non yet processed elements.
}
You are still modifying the index of elements ahead, but you are moving backwards, now.
In Visual Studio, you can use the forr code snippet to create a reverse for-loop. Type
forr <tab> <tab>.
(and of course there is the for code snippet for a normal for loop. It will increment the index with i++ instead of i += 1.)
Also, if the list is very long and you are removing many elements, it is worth to think about performance. This approach could move around a great number of elements. Copying the elements you want to keep to a new list (initialized with an appropriate initial capacity), will be more performing in this case.
Related
My assignment is to create a string list that has at least two matching values and then to prompt the user to input one of those values and then I am to display the index or indices of that value entered.
I seem to have figured out how to get the desired indices to show, but I also need to have a statement in the event the value entered is not in the list and when I do an else, it messes things up. Looking for some help on this!
So this does what I want but without the else statement:
using System;
using System.Collections.Generic;
class Program
{
static void Main(string[] args)
{
List<string> mprovinces = new List<string> { "Nova Scotia", "New Brunswick", "Prince Edward Island", "Nova Scotia" };
Console.WriteLine("Enter one of the following maritime provinces: \nNova Scotia, \nNew Brunswick, \nPrince Edward Island\n");
string input2 = Console.ReadLine();
for (int i = 0; i < mprovinces.Count; i++)
{
bool match = mprovinces[i] == input2;
if (match)
{
Console.WriteLine(i);
}
}
}
}
But when I add an else statement and I enter a value that is in the list it provides more data than I want:
using System;
using System.Collections.Generic;
class Program
{
static void Main(string[] args)
{
List<string> mprovinces = new List<string> { "Nova Scotia", "New Brunswick", "Prince Edward Island", "Nova Scotia" };
Console.WriteLine("Enter one of the following maritime provinces: \nNova Scotia, \nNew Brunswick, \nPrince Edward Island\n");
string input2 = Console.ReadLine();
for (int i = 0; i < mprovinces.Count; i++)
{
bool match = mprovinces[i] == input2;
if (match)
{
Console.WriteLine(i);
}
else
{
Console.WriteLine("Sorry, this is not in the list");
}
}
}
}
Since the "Sorry" message is inside of the for loop you will show it for EVERY index that does not exactly match your input2. You need to pull the match value out of the for loop and check it once.
var matchIndex = -1; // can never get a -1 so it's a good default to check for later
for (int i = 0; i < mprovinces.Count; i++)
{
if (mprovinces[i] == input2)
{
matchIndex = i;
break; // break out of loop
}
}
if (matchIndex >= 0) // again a valid index will never be below 0
{
Console.WriteLine("Index: " + matchIndex);
}
else
{
Console.WriteLine("Sorry, this is not in the list");
}
I'm not sure exactly what you want to show. If you only want to show the FIRST index that matches then the above code will work. If you want to show EVERY index that matches then this would work.
EDIT: I have changed this function to not use a string to keep track of the list. It just shows the matching indexes as they appear.
bool matchExists = false;
for (int i = 0; i < mprovinces.Count; i++)
{
if (mprovinces[i] == input2)
{
matchExists = true;
Console.WriteLine(i);
}
}
if (matchExists == false)
{
Console.WriteLine("Sorry, this is not in the list");
}
E.g. If we have an array [1,2,3,4,6,7,8] then 1 then 2 then 3 then 4 are all consecutive but 6 is not, so that's the first non-consecutive number.
If the whole array is consecutive then return null .
The array will always have at least 2 elements 1 and all elements will be numbers. The numbers will also all be unique and in ascending order. The numbers could be positive or negative and the first non-consecutive could be either too. please help me finish this code i am new in programming. My code:
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
namespace _2katas
{
public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
private void button1_Click(object sender, EventArgs e)
{
var input = this.txtInput.Text;
var numarray = input.Split(',');
int firstValue = Convert.ToInt32(numarray[0]);
for (var i = 0; i < numarray.Length; i++)
{
if (Convert.ToInt32(numarray[i]) - i != firstValue)
{
lblPrint.Text = "";
}
else
{
lblPrint.Text = "";
}
if (this.rdbConsecutive.Checked == true)
{
lblKataRunning.Text = "Consecutive";
}
else if (this.rdbStripCleaning.Checked == true)
{
lblKataRunning.Text = "Strip Cleaning";
}
}
}
}
}
Let's extract a method:
Find the first element of an array that is not consecutive ...
If the whole array is consecutive then return null
We can implement it like this:
private static string FirstInconsecutive(string data) {
var array = data.Split(',');
if (array.Length <= 0)
return null; //TODO: what shall we return on empty array?
if (!int.TryParse(array[0], out int delta))
return array[0];
for (int i = 1; i < array.Length; ++i)
if (!int.TryParse(array[i], out int value) || value - i != delta)
return array[i];
return null;
}
Usage:
string result = FirstInconsecutive(txtInput.Text);
Please note int.TryParse which helps to return the right answer "ABC" on an input like "1, 2, 3, ABC, 4, 6, 7, 8" (user input txtInput.Text can contain any string)
A linq solution just for the fun of it:
static int? FindFirstNonConsecutive(IEnumerable<int> arr)
{
var nonConsecutiveInfo =
arr.Select((i, index) => new {Index = index, Delta = i - index})
.FirstOrDefault(t => t.Delta != arr.First());
return nonConsecutiveInfo?.Delta + nonConsecutiveInfo?.Index;
}
Note that this will only work finding non consecutive numbers in ascending order as per requirements.
Two numbers are not consecutive if the left ones + 1 <> the right one.
Check with something like this, note that you have to change your boundary checks:
for (var i = 0; i < numarray.Length - 1; i++)
{
if (Convert.ToInt32(numarray[i]) + 1 != Convert.ToInt32(numarray[i+1]))
Update your condition as below for loop and it will work. I would suggest you to have separate function so that it could be reusable if needed elsewhere in code.
Here start your loop from i = 1 and compare numarray[i-1] + 1 != numarray[i] values.
You can convert your sting[] to int[] with var numarray = input.Split(',').Select(x => Convert.ToInt32(x)).ToArray(); and use it with IsConsecutive(numarray) as per button1_Click code.
You can get first non-consecutive value with minor modification in return type and return statement as shown in GetFirstNonConsecutiveValue().
public bool IsConsecutive(int[] numarray)
{
for (int i = 1; i < numarray.Length; i++)
{
if (numarray[i-1] + 1 != numarray[i])
{
return false;
}
}
return true;
}
public int? GetFirstNonConsecutiveValue(int[] numarray)
{
for (int i = 1; i < numarray.Length; i++)
{
if (numarray[i-1] + 1 != numarray[i])
{
return numarray[i];
}
}
return null;
}
private void button1_Click(object sender, EventArgs e)
{
var input = this.txtInput.Text;
var numarray = input.Split(',').Select(x => Convert.ToInt32(x)).ToArray();
var nonConsecutiveValue = GetFirstNonConsecutiveValue(numarray);
if (nonConsecutiveValue != null)
{
// nonConsecutiveValue is first non consecutive value.
}
else
{
// sequence is consecutive.
}
}
One way to go.
string rawData = "1,2,3,4,6,7,8,9";
IEnumerable<int> data = rawData.Split(',').Select(v => Convert.ToInt32(v));
IEnumerable<int> all = Enumerable.Range(data.Min(), data.Max() - data.Min() + 1);
IEnumerable<int> diff = all.Except(data);
if (diff.Count() == 0)
{
return null;
}
return data.ElementAt(all.ToList().IndexOf(diff.First()))
NB Not thoroughly tested.
Just test diff for being empty to get the numbers are consecutive
I have a List<Keyword> where Keyword class is:
public string keyword;
public List<int> ids;
public int hidden;
public int live;
public bool worked;
Keyword has its own keyword, a set of 20 ids, live by default is set to 1 and hidden to 0.
I just need to iterate over the whole main List to invalidate those keywords whose number of same ids is greater than 6, so comparing every pair, if the second one has more than 6 ids repeated respect to the first one, hidden is set to 1 and live to 0.
The algorithm is very basic but it takes too long when the main list has many elements.
I'm trying to guess if there could be any method I could use to increase the speed.
The basic algorithm I use is:
foreach (Keyword main_keyword in lista_de_keywords_live)
{
if (main_keyword.worked) {
continue;
}
foreach (Keyword keyword_to_compare in lista_de_keywords_live)
{
if (keyword_to_compare.worked || keyword_to_compare.id == main_keyword.id) continue;
n_ids_same = 0;
foreach (int id in main_keyword.ids)
{
if (keyword_to_compare._lista_models.IndexOf(id) >= 0)
{
if (++n_ids_same >= 6) break;
}
}
if (n_ids_same >= 6)
{
keyword_to_compare.hidden = 1;
keyword_to_compare.live = 0;
keyword_to_compare.worked = true;
}
}
}
The code below is an example of how you would use a HashSet for your problem. However, I would not recommend using it in this scenario. On the other hand, the idea of sorting the ids to make the comparison faster still.
Run it in a Console Project to try it out.
Notice that once I'm done adding new ids to a keyword, I sort them. This makes the comparison faster later on.
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Text;
namespace KeywordExample
{
public class Keyword
{
public List<int> ids;
public int hidden;
public int live;
public bool worked;
public Keyword()
{
ids = new List<int>();
hidden = 0;
live = 1;
worked = false;
}
public override string ToString()
{
StringBuilder s = new StringBuilder();
if (ids.Count > 0)
{
s.Append(ids[0]);
for (int i = 1; i < ids.Count; i++)
{
s.Append(',' + ids[i].ToString());
}
}
return s.ToString();
}
}
public class KeywordComparer : EqualityComparer<Keyword>
{
public override bool Equals(Keyword k1, Keyword k2)
{
int equals = 0;
int i = 0;
int j = 0;
//based on sorted ids
while (i < k1.ids.Count && j < k2.ids.Count)
{
if (k1.ids[i] < k2.ids[j])
{
i++;
}
else if (k1.ids[i] > k2.ids[j])
{
j++;
}
else
{
equals++;
i++;
j++;
}
}
return equals >= 6;
}
public override int GetHashCode(Keyword keyword)
{
return 0;//notice that using the same hash for all keywords gives you an O(n^2) time complexity though.
}
}
class Program
{
static void Main(string[] args)
{
List<Keyword> listOfKeywordsLive = new List<Keyword>();
//add some values
Random random = new Random();
int n = 10;
int sizeOfMaxId = 20;
for (int i = 0; i < n; i++)
{
var newKeyword = new Keyword();
for (int j = 0; j < 20; j++)
{
newKeyword.ids.Add(random.Next(sizeOfMaxId) + 1);
}
newKeyword.ids.Sort(); //sorting the ids
listOfKeywordsLive.Add(newKeyword);
}
//solution here
HashSet<Keyword> set = new HashSet<Keyword>(new KeywordComparer());
set.Add(listOfKeywordsLive[0]);
for (int i = 1; i < listOfKeywordsLive.Count; i++)
{
Keyword keywordToCompare = listOfKeywordsLive[i];
if (!set.Add(keywordToCompare))
{
keywordToCompare.hidden = 1;
keywordToCompare.live = 0;
keywordToCompare.worked = true;
}
}
//print all keywords to check
Console.WriteLine(set.Count + "/" + n + " inserted");
foreach (var keyword in set)
{
Console.WriteLine(keyword);
}
}
}
}
The obvious source of inefficiency is the way you calculate intersection of two lists (of ids). The algorithm is O(n^2). This is by the way problem that relational databases solve for every join and your approach would be called loop join. The main efficient strategies are hash join and merge join. For your scenario the latter approach may be better I guess, but you can also try HashSets if you like.
The second source of inefficiency is repeating everything twice. As (a join b) is equal to (b join a), you do not need two cycles over the whole List<Keyword>. Actually, you only need to loop over the non duplicate ones.
Using some code from here, you can write the algorithm like:
Parallel.ForEach(list, k => k.ids.Sort());
List<Keyword> result = new List<Keyword>();
foreach (var k in list)
{
if (result.Any(r => r.ids.IntersectSorted(k.ids, Comparer<int>.Default)
.Skip(5)
.Any()))
{
k.hidden = 1;
k.live = 0;
k.worked = true;
}
else
{
result.Add(k);
}
}
If you replace the linq with just the index manipulation approach (see the link above), it would be a tiny bit faster I guess.
namespace Palindrome
{
class Program
{
public static bool IsPalindrome(string s)
{
int min = 0;
int max = s.Length - 1;
while (true)
{
if (min > max) // True if we've compared up to, and then gone passed the middle of the string.
return true;
if (char.ToLower(s[min++]) != char.ToLower(s[max]))
return false;
}
}
static void Main(string[] args)
{
string [] words = {
"civic",
"deified",
// ...
"stats",
"tenet",
};
foreach (string value in words)
{
Console.WriteLine("{0} = {1}", value, IsPalindrome(value));
}
Console.WriteLine("\nPress any key to continue...");
Console.ReadKey(true); }
}
}
The program checks to see if the words in the words array are Palindromes (words spelled the same forwards as they are backwards).
The foreach loop in Main passes each of the words in the array to the IsPalindrome() function; which tests the word, and returns True or False accordingly.
As each word in the current array is a Palindrome, when the program is run, it should output all of the current words, followed by True. However, it gives me False. Why is that?
Seems to me like you've forgotten to decrease the value of max; i.e. the following:
if (char.ToLower(s[min++]) != char.ToLower(s[max]))
... should probably be:
if (char.ToLower(s[min++]) != char.ToLower(s[max--]))
Anyway, you should be able to clear this up pretty quickly if you run through it in debug mode, and step through your code.
Try
if (char.ToLower(s[min++]) != char.ToLower(s[max--]))
return false;
I think you forgot to decrement your max variable.
Now you're just comparing each letter with the last.
You already got answers about whats wrong with your code. Here's an cleaner solution option(if you dont need any performance optimizations):
public static bool IsPalindrome(string s)
{
char[] array = s.ToCharArray();
Array.Reverse(array);
string backwards = new string(array);
return s.Equals(backwards, StringComparison.OrdinalIgnoreCase);
}
You have to decrease your max value.
For another method of testing.
var input = "abba";
var output = input.ToCharArray().Reverse().Aggregate("",(x,y) => x + y));
return input.Equals(output, StringComparison.OrdinalIgnoreCase);
here you go, a better culture/case insensitive version
using System.Globalization;
bool IsPalindrome(string value, StringComparer comparer = null)
{
if (s == null)
{
throw new ArgumentNullException("value");
}
if (comparer == null)
{
comparer = StringComparer.CurrentCultureIgnoreCase;
}
var elements = new List<string>();
var m = StringInfo.GetTextElementEnumerator(value);
while (m.MoveNext())
{
elements.Add(m.GetTextElement());
}
var i = 0;
var j = elements.Count - 1;
var limit = elements.Count / 2;
for(; i <= limit; i++, j--)
{
if (!comparer.Equals(elements[i], elements[j]))
{
return false;
}
}
return true;
}
For homework assignment we have to program a Intersection merge of 2 ArrayLists. I have done it using the following code
public void Intersection()
{
foreach (object obj1 in Developed)
{
Apps xApp = (Apps)obj1;
foreach (object obj2 in DPloyed)
{
Apps yApp = (Apps)obj2;
if (xApp.CompareName(yApp) == 0)
{
Inter.Add(yApp);
}
}
}
}
I would like to implement it rather using the while loop but the following code seems to keep missing elements in the list. It puts the first elements in the new intersection list but once the length of developed is increased from 1 element to 5 elements or more it does not add the new elements.
public void Intersection()
{
int i = 0;
int j = 0;
while (i < Developed.Count && j < DPloyed.Count)
{
Apps curA = (Apps)Developed[i];
Apps curB = (Apps)DPloyed[j];
if (curA.CompareName(curB) == 0)
{
Inter.Add(curA);
i++;
j++;
}
else if (curA.CompareName(curB) < 0)
{
i++;
}
else
j++;
}
}
Any help as to why the while loop does not work would be appreciated.
Thanks
Do this
while (i < Developed.Count || j < DPloyed.Count)
because may be both list may be having different Count.
and you need to put extra checks inside loop for indexes so that you don't get Index out of Range Exception.
Problem was not in the actual code for the merges. Problem found in my compare methods.