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First repeating element

(4 posts)

1. 

   geek4u
   guest
   Posted 2 years ago #
   
   

   Given an array of n numbers in which all the members are less than or equal to k (k<n). device an algorithm of order O(k) to find the first repeating element.

2. 

   Sandeep
   Moderator
   Posted 2 years ago #
   
   

   Please see http://geeksforgeeks.org/?p=1781. Since the range is given in your question also, you can easily modify the code for integers.

3. 

   crazyFrog
   Member
   Posted 2 years ago #
   
   

   Assuming that all numbers are positive (may include 0) then its simple:
   iterate through the array and increase the count of the element appearing till you get all 1s, as soon as you get 2 return that same element.
   Since there are only k distinct elements, then at worst case you will have to traverse k+1 times which is again O(k).

4. 

   gvk
   guest
   Posted 4 months ago #
   
   

   #include<stdio.h>
   #define N 15
   #define K 9 //elements lie between 0 to 9
   
   int *init_count(int *);
   int index_first_non_repeating(int *);
   
   int main()
   {
       int a[] = {0,1,2,1,2,3,4,5,3,7,8,9,9,6,0}; // array has N elements
       int i = index_first_non_repeating(a);
       printf("First non-repeating integer in array is: %d\n",i);
       printf("Element at that index is is: %d\n",a[i]);
       return 0;
   }
   
   int index_first_non_repeating(int *a)
   {
       int *b = init_count(a);
       int i;
       for(i=0;i<N;i++)
       {
           if(b[a[i]] == 1)
               return i;
       }
       return -1;
   }
   
   int *init_count(int *a)
   {
       int *b = (int *)calloc(sizeof(int),(K+1));
       int i;
       for(i=0;i<N;i++)
           b[a[i]]++;
       return b;
   }

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