减少时间复杂度

Question

The question asked is using

struct match_score
{
char country[20];
int score;
};

wherein the structure is related to a batsman's score and the country he scored against. We have to find the country against which he has the highest average.

I have written a code whose time complexity is O(n^2) Can anyone suggest me how to reduce the time complexity to O(nlogn) or O(n)

Code with O(n^2)

#include <stdio.h>
#include <string.h>
struct match_score
{ 
  char country[20];
  int score;
};
char *func(struct match_score *array,int len); 
main()
{
    struct match_score scores[]={
        {"Pakistan",23},
        {"India",52},
        {"Pakistan",40},
        {"India",22},
        {"Australia",80}
    };
    char *max_avg=func(scores,5);
    printf("%s",max_avg);

}
char *func(struct match_score *array,int len)
{

 int i,j,average[20],avg,l,max=0,max_num;
 char co[20];
 for(i=0;i<len;i++)
 {
     average[i]=0;
 }
 for(i=0;i<len;i++)
 {
      avg=0;
      l=0;
      strcpy(co,"");
      strcpy(co,array[i].country);
      for(j=0;j<len;j++)
      {
          if(strcmp(array[j].country,co)==0)
          {
              l++;
              avg+=array[j].score;
          } 
      }
      average[i]=avg/l;
   }

   for(i=0;i<len;i++)
   {
      if(average[i]>max)
      {
         max=average[i];
         max_num=i;
      }
   }
   for(i=0;i<len;i++)
   {
      printf("%d %d\n",i,average[i]);
   }
   return array[max_num].country;
}

Answer 1

The area where you hit n^2 is here;

 for(i=0;i<len;i++)
 {
      for(j=0;j<len;j++)
      {
          if(strcmp(array[j].country,co)==0)

All this is doing is searching for duplicate countries in your array. If you sort the array, at a cost of n log n, you can find duplicates in order n. This leaves you with a new complexity of o(n log n)

Answer 2

You could use a temporary collection in which you store the averages, then iterate over that to find the largest. This will use more space, but will be O(2n) as you have to loops in a row instead of nested.

Answer 3

If you sort the arry, your complicaation reduce significanty. searching a number in a sorted arry is much quicker....

Btw, you should have explained your algorithem and your code, or at least give some notes...