Tuesday, 23 December 2014

Hackerrank Counting Sort 1 Solution

Problem Statement
Comparison Sorting
Quicksort usually has a running time of n*log(n), but is there an algorithm that can sort even faster? In general, this is not possible. Most sorting algorithms are comparison sorts, i.e., they sort a list just by comparing the elements with one another. A comparison sort algorithm cannot beat n log(n) (worst-case) running time, since n log(n) represents the minimum number of comparisons needed to know where to place each element. For more details, you can see these notes (PDF).
Alternative Sorting
However, for certain types of input, it is more efficient to use a non-comparison sorting algorithm. This will make it possible to sort lists even in linear time. These challenges will cover Counting Sort, a fast way to sort lists where the elements have a small number of possible values, such as integers within a certain range. We will start with an easy task - counting.

Challenge
Given a list of integers, can you count and output the number of times each value appears?
Hint: There is no need to sort the data, you just need to count it.
Input Format
There will be two lines of input:
  • n - the size of the list
  • ar - n space separated numbers that makes up the list
Output Format
Output the number of times every number from 0 to 99 (inclusive) appears in the list.
Constraints
100 <= n <= 106
0 <= x < 100 , x ∈ ar
Sample Input
100
63 25 73 1 98 73 56 84 86 57 16 83 8 25 81 56 9 53 98 67 99 12 83 89 80 91 39 86 76 85 74 39 25 90 59 10 94 32 44 3 89 30 27 79 46 96 27 32 18 21 92 69 81 40 40 34 68 78 24 87 42 69 23 41 78 22 6 90 99 89 50 30 20 1 43 3 70 95 33 46 44 9 69 48 33 60 65 16 82 67 61 32 21 79 75 75 13 87 70 33 
Sample Output
0 2 0 2 0 0 1 0 1 2 1 0 1 1 0 0 2 0 1 0 1 2 1 1 1 3 0 2 0 0 2 0 3 3 1 0 0 0 0 2 2 1 1 1 2 0 2 0 1 0 1 0 0 1 0 0 2 1 0 1 1 1 0 1 0 1 0 2 1 3 2 0 0 2 1 2 1 0 2 2 1 2 1 2 1 1 2 2 0 3 2 1 1 0 1 1 1 0 2 2 
Explanation
the output states that 0 appears 0 times.
1 appears 2 times.
2 appears 0 times.
and so on in the given input array.

Source Code:
 #include <cmath>  
 #include <cstdio>  
 #include <vector>  
 #include <iostream>  
 #include <algorithm>  
 using namespace std;  
 int main() {  
   /* Enter your code here. Read input from STDIN. Print output to STDOUT */    
   long long arr[1000000]={0},n,i,j,k,x;  
   cin>>n;  
   for(i=0;i<n;i++){  
     cin>>x;  
     arr[x]++;  
   }  
   for(i=0;i<100;i++)  
     {  
     cout<<arr[i]<<" ";  
   }  
   cout<<endl;  
   return 0;  
 }  

** The above solution is my own code and it may not be the optimal solution or optimal way to approach the problem but it passes all the testcases in Hackerrank. So if you have any optimal approaches feel free to paste the code as the comment below..... :) :) :)


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