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  1. Practice
  2. Algorithms
  3. Implementation
  4. Circular Array Rotation
  5. Discussions

Circular Array Rotation

  • Dinesh1306 + 2 comments

    In my solution the index are within the boundaries.

    • rn27in + 0 comments

      Thanks a ton Dinesh. Beautiful solution. I initially used brute force without understanding the rotation pattern.

      Learnt something new. Your blog is really good

      Cheers

    • hackernitp + 13 comments
      #include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;


int main(){
    int n;
    int k;
    int q;
    cin >> n >> k >> q;
    vector<int> a(n);
    for(int a_i = 0;a_i < n;a_i++){
       cin >> a[a_i];
    }
    
    for(int i=0;i<k;i++){
        for(int j=0;j<n;j++){
            if(j+1!=n)
            {
                a[j+1]=a[j];
                
            }
               else
               {
                   a[0]=a[n-1];
               }
        }
    }
    for(int a0 = 0; a0 < q; a0++){
        int m;
        cin >> m;
    cout<<a[m]<<endl;}
    return 0;
}

      can you plz tell me what is wrong with my code???

      • JamesTre + 0 comments

        Hi, dk201966. Probably you are facing problems because the order you are doing the changes. If you copy the value from the 1st position to the 2nd one and, after this, you copy the 2nd to the 3rd, at the end you will have all the positions with the 1st value. And don't forget saving the last value before overwriting it! PS: you'll probably face other issues with this challenge...

      • moguz00 + 1 comment

        Dude please fix your "include"s they seem ugly :)

      • pratikgk98 + 1 comment

        The main problem in the code is the order of the for loop used for rotating the elenets in the array. You should store the last element value in some temporary variable..and then use a decreasing counter in the mentioned for loop ..then u can store the value in temporary variable to the first element The error in ur code of overwriting values is eleminated by this code!👍

        • upendra28 + 3 comments

          why my code gives wrong answers ...? 

          vector <int> circularArrayRotation(vector <int> a, vector <int> m,int n,int k, int q) 
{
        while(k!=0)
        {
            int end=a[n-1];
            for(int i=n-2;i>=0;i--)
            {
                a[i+1]=a[i];
            }
            a[0]=end;
            k--;
        }
        
    return a;
}
          • sankarasettyavi1 + 0 comments

            you need to return q not a.

          • anisaxena53 + 0 comments

            you are not supposed to print the whole array a but only the elements at positions in queries

          • abhilash_brains1 + 1 comment

            how come!, It's not working???

            • nilanjan172nsvi1 + 0 comments

              if you try to interchange the value,t then it does not work,

      • mykz950 + 0 comments

        if(j+1!=n-1)

      • Saurav_Gaikwad1 + 0 comments

        in your code there is assignment of values....shifting of values is absent..

      • S_A_G + 0 comments

        hi Change your condition as a[j-1]=a[j]; and j=n-1;j>=0;j-- in for loop

      • vikram777 + 0 comments

        your code is wrong due to elae statement

      • kusaalpokharel + 0 comments

        I did the same and realized the values of the elements of the array that you assign later has already replaced the other element in the array. For eg: a[1]=a[0] then a[2]=a[1]=a[0] which is equal to each other

      • wildmud + 2 comments
        #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 */ 
    int n,k,q,i,s=0,e=0, t=0,b;
    cin>>n>>k>>q;
    int a[n];
    for(i=0;i<n;i++)
    {
        cin>>a[i];
        
    }
    
    k=k%n;
    
    s=0,e=n-k-1;
    while(s<e)
    {
       t=a[s];
        a[s]=a[e];
        a[e]=t;
        s++;e--;
        
    }
  
     s=n-k,e=n-1;
    while(s<e)
    {
       t=a[s];
        a[s]=a[e];
        a[e]=t;
        s++;e--;
        
    }
    
     s=0,e=n-1;
    while(s<e)
    {
       t=a[s];
        a[s]=a[e];
        a[e]=t;
        s++;e--;
        
    }
    
     for(i=0;i<q;i++)
    {
        cin>>b;
         cout<<a[b]<<endl;
        
    }
    
    
    
    
    return 0;
}
        • rvrishav7 + 0 comments
          faster than urs i guess.. happy coding
#include<bits/stdc++.h>

using namespace std;


int main() {
   long long int k,n,q;
    cin>>n>>k>>q;
    k=k%n;
   long long int i,ar[n],x,s=0;
    for(i=0;i<n;i++)
        cin>>ar[i];
    for(i=1;i<=q;i++)
    {
          cin>>x;
     s=n-k+x;
     if(s<n)
         cout<<ar[s]<<endl;
     else if(s>=n)
     { s=s-n;
         cout<<ar[s]<<endl;
    }}

    return 0;
}
        • aiswarya110498 + 0 comments

          Thank you very much..passed all test cases.

      • rvrishav7 + 2 comments
        #include<bits/stdc++.h>

using namespace std;


int main() {
   long long int k,n,q;
    cin>>n>>k>>q;
    k=k%n;
   long long int i,ar[n],x,s=0;
    for(i=0;i<n;i++)
        cin>>ar[i];
    for(i=1;i<=q;i++)
    {
          cin>>x;
     s=n-k+x;
     if(s<n)
         cout<<ar[s]<<endl;
     else if(s>=n)
     { s=s-n;
         cout<<ar[s]<<endl;
    }}

    return 0;
}

        it will work

        • NiceBuddy + 0 comments

          simpler one:

          #include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>

int main()
{
    int n; std::cin >> n; // array size
    int k; std::cin >> k; //no of rotations
    int q; std::cin >> q;

    std::vector<int> vec;
    vec.reserve(n);
    std::copy_n(std::istream_iterator<int>(std::cin), 
                n, back_inserter(vec));
    k %= n;
    k = n-k;
    std::rotate(vec.begin(), vec.begin()+k,vec.end());

    while(q--)
    {
        int index; std::cin >> index;
        std::cout << vec[index]  << std::endl;
    }
    return 0;
}
        • umangsomtiya8083 + 0 comments

          why are you taking modulus of k???

      • rvrishav7 + 0 comments

        refer to my code

      • rvrishav7 + 0 comments
        #include<bits/stdc++.h>

using namespace std;


int main() {
   long long int k,n,q;
    cin>>n>>k>>q;
    k=k%n;
   long long int i,ar[n],x,s=0;
    for(i=0;i<n;i++)
        cin>>ar[i];
    for(i=1;i<=q;i++)
    {
          cin>>x;
     s=n-k+x;
     if(s<n)
         cout<<ar[s]<<endl;
     else if(s>=n)
     { s=s-n;
         cout<<ar[s]<<endl;
    }}

    return 0;
}

        refer this

      • nilanjan172nsvi1 + 0 comments

        same to you. but if you dry run the code ,then can you understand what is wrong with the code !!