Finding duplicate integers in an array and display how many times they occurred

Question

I m working on a code that prints out duplicated integers from an array with the number of their occurrence  I m not allowed to use LINQ  just a simple code  I think I m so close but confused about how to get a correct output    class Program       static void Main string   args                              int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12            int count   1          for  int i   0  i  lt  array Length  i                          for  int j   i  j  lt  array Length - 1   j                                  if array j     array j 1                     count   count   1                            Console WriteLine   t n     array i     occurse    count               Console ReadKey

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class Program       static void Main string   args                int   arr     2  3  2  4  5  12  2  3  3  3  12            List lt int gt  nums   new List lt int gt             List lt int gt  count   new List lt int gt             nums Add arr 0            count Add 1           for  int i   1  i  lt  arr Length  i                           if nums Contains arr i                                  count nums IndexOf arr i       1                            else                               nums Add arr i                    count Add 1                                    for int x  0  x lt nums Count x                          Console WriteLine  number   nums x    Count     count x                      Console Read

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You made a minor mistake of using J instead of i      class Program       static void Main string   args                              int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12            int count   1          for  int i   0  i  lt  array Length  i                          for  int j   i  j  lt  array Length - 1   j                                 if array i     array j 1                     count   count   1                            Console WriteLine   t n     array i     occurse    count               Console ReadKey

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I m in agreement that using Dictionary is better running time performance then nested for loops  O n  vs O n 2    However to address OP  here is a solution where a HashSet is used to prevent repeating the counting of integers already counted  such as integer 5 in example array   static void Main string   args                      int   A     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12         var set   new HashSet lt int gt         for  int i   0  i  lt  A Length - 1  i              int count   0          for  int j   i  j  lt  A Length - 1  j                  if  A i     A j   1   amp  amp   set Contains A i                    count                      set Add A i            if  count  gt  0                Console WriteLine   0  occurs  1  times   A i   count   1               Console ReadKey

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public static void Main string   args       Int   array    10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12    List lt int gt  doneNumbers   new List lt int gt       for  int i   0  i  lt  array Length - 1  i            if  doneNumbers Contains array i                    int currentNumber   array i            int count   0           for  int j   i  j  lt  array Length  j                            if currentNumber    array j                                   count                                       Console WriteLine   t n     currentNumber         occurs         count         times             doneNumbers Add currentNumber            Console ReadKey

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You can check the following codes  The codes are working    class Program       static void Main string   args          int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12          int count   1        for  int i   0  i  lt  array Length  i              for  int j   i   1  j  lt  array Length  j                 if  array j     array j               count   count   1                    Console WriteLine   t n     array i      out of     count           Console ReadKey

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using System  using System Collections Generic   namespace ConsoleApp1            lt summary gt          How do you find the duplicate number on a given integer array           lt  summary gt      class Program               static void Main string   args                        int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12                 Dictionary lt int  int gt  duplicates   FindDuplicate array                Display duplicates                Console ReadLine                       private static Dictionary lt T  int gt  FindDuplicate lt T gt  IEnumerable lt T gt  source                        HashSet lt T gt  set   new HashSet lt T gt                 Dictionary lt T  int gt  duplicates   new Dictionary lt T  int gt                  foreach  var item in source                                if   set Add item                                         if  duplicates ContainsKey item                                                 duplicates item                                               else                                               duplicates Add item  2                                                                      return duplicates                     private static void Display Dictionary lt int  int gt  duplicates                        foreach  var item in duplicates                                Console WriteLine    item Key   item Value

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Just use the code below no need to use dictionary or ArrayList Hope this helps     public static void Main string   args                      int    array  new int   10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12       Array Sort array       for  int i   0  i  lt  array Length  i                  int count   1 k -1          for  int j   i 1  j  lt  array Length  j                                 if array i     array j                                         count                        k j-1                                    else break                    Console WriteLine   t n     array i     ---------- gt     count                       if k  -1              i k 1

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Use Group by   int   values   new    1 2 3 4 5 4 4 3    var groups   values GroupBy v   gt  v   foreach var group in groups      Console WriteLine  Value  0  has  1  items   group Key  group Count

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int   array     10  5  10  2  2  3  4  5  5  7  7  8  9  7  12  12    Dictionary lt int  int gt  duplicateNumbers   new Dictionary lt int  int gt     int count 1  for  int i   0  i  lt  array Length  i          count 1      if  duplicateNumbers ContainsKey array i                  for  int j   i  j  lt  array Length-1  j                          if  array i     array j 1                                 count                                                                if  count  gt  1                        duplicateNumbers Add array i   count                     foreach  var num in duplicateNumbers        Console WriteLine  Duplicate numbers  NUMBER- 0   OCCURRENCE-  1   num Key num Value

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class Program       static void Main string   args                int   arr   new int     10  20 20  30  10  50  50 9           List lt int gt  listadd   new List lt int gt              for  int i 0  i  lt arr Length i                         int count   0              int flag   0               for int j 0  j  lt  arr Length  j                                  if  listadd Contains arr i      false                                          if  arr i     arr j                                                 count                                                               else                                       flag   1                                               listadd Add arr i                if flag  1              Console WriteLine  No of occurance  0   t 1    arr i   count                     Console ReadLine

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int   arr     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12    var result   arr GroupBy x   gt  x  Select x   gt  new   key   x Key  val   x Count              foreach  var item in result        if item val  gt  1                                Console WriteLine  Duplicate value    0    item key           Console WriteLine  MaxCount    0    item val             Console ReadLine

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public class Program       public static void Main string   args                int   arr   new int   10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12            int numberOfDuplicate   0          int arrayLength   arr Length           for int i 0  i  lt  arrayLength  i                             for int j   1  j  lt  arrayLength  j                                  if j  lt  i  amp  amp  arr j   arr i                                      break                                   else if i    j  amp  amp  arr i   arr j                                      Console Write  duplicate   arr  0    1 --arr  2    3  n  i arr i  j arr j                      numberOfDuplicate                      break                                                   Console Write  Total duplicate element in an array  arr  is  0  n   numberOfDuplicate

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This is the answer that helps you to find the duplicate integer values using Forloop and it will return only the repeated values apart from its times of occurences       public static void Main string   args                  Array list to store all the duplicate values         int   ary     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12            ArrayList dup   new ArrayList             for  int i   0  i  lt  ary Length  i                          for  int j   i   1  j  lt  ary Length  j                                  if  ary i  Equals ary j                                          if   dup Contains ary i                                                  dup Add ary i                                                                            Console WriteLine  The numbers which duplicates are            DisplayArray dup             public static void DisplayArray ArrayList ary                  loop through all the elements         for  int i   0  i  lt  ary Count  i                          Console Write ary i                            Console WriteLine            Console ReadKey

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Let s take a look at a simpler example   Let s say we have the array  0  0  0  0    What will your code do   It will first look to see how many items after the first item are equal to it   There are three items after the first that are equal to it   Then it goes to the next item  and looks for all items after it that are equal to it   There are two   So far we re at 5  and we haven t even finished yet  we have one more to add   but there are only four items in the whole array   Clearly we have an issue here   We need to ensure that when we ve searched the array for duplicates of a given item that we don t search through it again for that same item   While there are ways of doing that  this fundamental approach is looking to be quite a lot of work   Of course  there are different approaches entirely that we can take   Rather that going through each item and searching for others like it  we can loop through the array once  and add to a count of number of times we ve found that character   The use of a Dictionary makes this easy   var dictionary   new Dictionary lt int  int gt      foreach  int n in array        if   dictionary ContainsKey n           dictionary n    0      dictionary n         Now we can just loop through the dictionary and see which values were found more than once   foreach var pair in dictionary      if pair Value  gt  1          Console WriteLine pair Key     This makes the code clear to read  obviously correct  and  as a bonus  quite a lot more efficient than your code  as you can avoid looping through the collection multiple times

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int copt   1  int element   0  int   array     1  2  3  3  3  3  3  3  3  3  3  4  5    for  int i   0  i  lt  array Length  i         for  int j   i   1  j  lt  array Length - 1  j                if  array i     array j                      element   array i             copt              break                   Console WriteLine  the repeat element is  0  and it s appears  1  times    element  copt   Console ReadKey         the output is the element is 3 and appears 9 times

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This approach  fixed up  will give the correct output  it s highly inefficient  but that s not a problem unless you re scaling up dramatically    int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12    for  int i   0  i  lt  array Length  i          int count   0      for  int j   0  j  lt  array Length   j                 if array i     array j             count   count   1            Console WriteLine   t n     array i      occurs     count       Console ReadKey        I counted 5 errors in the OP code  noted below   int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12    int count   1                                       1  have to put  count  in the inner loop so it gets reset                                                     2  have to start count at 0 for  int i   0  i  lt  array Length  i          for  int j   i  j  lt  array Length - 1   j        3  have to cover the entire loop                                                     for  int j 0   j lt array Length   j                 if array j     array j 1                     4  compare outer to inner loop values                                                     if  array i     array j             count   count   1            Console WriteLine   t n     array i     occurse    count                                                       5  It s spelled  occurs         Console ReadKey        Edit   For a better approach  use a Dictionary to keep track of the counts   This allows you to loop through the array just once  and doesn t print duplicate counts to the console   var counts   new Dictionary lt int  int gt     int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12    for  int i   0  i  lt  array Length  i          int currentVal   array i       if  counts ContainsKey currentVal           counts currentVal         else         counts currentVal    1    foreach  var kvp in counts      Console WriteLine   t n     kvp Key     occurs     kvp Value

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This method counts a total number of duplicate elements in an array  public void DuplicateElementsInArray int   numbers                int count   0           for  int i   0  i  lt  numbers Length  i                           for  int j   i  j  lt  numbers Length - 1  j                                  if  numbers i     numbers j 1                                                                count                        break                                                                                          Console WriteLine  Total number of duplicate elements found in the array is   0    count

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static void printRepeating int   arr                               int size                  int i         Console Write  The repeating                           elements are             for  i   0  i  lt  size  i                    if  arr  Math Abs arr i     gt   0               arr  Math Abs arr i                       -arr  Math Abs arr i              else             Console Write Math Abs arr i

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Here is an answer that avoids using Dictionaries  Since the OP said he is not familiar with them  this might give him a little insight into what Dictionaries do   The downside to this answer is you have to enforce a limit on the max number in the array  and you can t have negative numbers  You d never actually use this version in real code   int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12    int   count   new int 13    foreach int number in array           using the index of count same way you d use a key in a dictionary     count number        foreach int c in count        int numberCount   count c       if numberCount  gt  0            Console WriteLine c     occurs     numberCount     times

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Since you can t use LINQ  you can do this with collections and loops instead   static void Main string   args                      int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12        var dict   new Dictionary lt int  int gt          foreach var value in array                if  dict ContainsKey value               dict value             else             dict value    1             foreach var pair in dict          Console WriteLine  Value  0  occurred  1  times    pair Key  pair Value       Console ReadKey

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Ok I have modified your code  This should do the job   class Program       static void Main string   args                int   array     10  5  10  2  2  3  4  5  5  6  7  8  9  11  12  12             for  int i   0  i  lt  array Length  i                          int count   0              for  int j   0  j  lt  array Length  j                                   if  array i     array j                       count   count   1                            Console WriteLine   t n     array i      occurs     count     times                      Console ReadKey

[c#] Finding duplicate integers in an array and display how many times they occurred

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