45.
Which data structures can be used to implement least recently used cache?

46.
. . . . . . . . is one of the most useful principles of enumeration in combinationatorics and discrete probability.

48.
What does the following code do?
#include<stdio.h>
#include<string.h>
void reverse_string(char *s)
{
     int len = strlen(s);
     int i,j;
     i=0;
     j=len-1;
     while(i < j)
     {
         char tmp = s[i];
         s[i] = s[j];
         s[j] = tmp;
         i++;
         j--;
     }
}
int main()
{
      char s[100] = "abcdefg";
      char t[100];
      strcpy(t,s);
      reverse_string(s);
      if(strcmp(t,s) == 0)
        printf("Yes");
      else
        printf("No");
      return 0;
}