CareerCup

// C++ program to implement your own tail 
#include <bits/stdc++.h> 
using namespace std; 
  
#define SIZE 100 
  
// Utility function to sleep for n seconds 
void sleep(unsigned int n) 
{ 
    clock_t goal = n * 1000 + clock(); 
    while (goal > clock()); 
} 
  
// function to read last n lines from the file 
// at any point without reading the entire file 
void tail(FILE* in, int n) 
{ 
    int count = 0;  // To count '\n' characters 
  
    // unsigned long long pos (stores upto 2^64 – 1 
    // chars) assuming that long long int takes 8  
    // bytes 
    unsigned long long pos; 
    char str[2*SIZE]; 
  
    // Go to End of file 
    if (fseek(in, 0, SEEK_END)) 
        perror("fseek() failed"); 
    else
    { 
        // pos will contain no. of chars in 
        // input file. 
        pos = ftell(in); 
  
        // search for '\n' characters 
        while (pos) 
        { 
            // Move 'pos' away from end of file. 
            if (!fseek(in, --pos, SEEK_SET)) 
            { 
                if (fgetc(in) == '\n') 
  
                    // stop reading when n newlines 
                    // is found 
                    if (count++ == n) 
                        break; 
            } 
            else
                perror("fseek() failed"); 
        } 
  
        // print last n lines 
        printf("Printing last %d lines -\n", n); 
        while (fgets(str, sizeof(str), in)) 
            printf("%s", str); 
    } 
    printf("\n\n"); 
}

Linux command to read last 10 lines of a file :

tail -n <number_of_lines> /path/to/file

create a queue with size 10, start reading the file line by line and as you do so, insert them in the queue, keeping on popping elements from the queue if max size reached. Towards the end you will have last ten lines of the file.

refer CTCI book,

String[] ans = new String[k];
int c = 0;
while(!feof(fp))
{
   fread(fp, buf);
   ans[c%k] = buf;
   c++;
  
}

return ans;

I just wrote this .. and I believe it is beautiful. From elegance perspective. Hence, sharing.

def tail_function( file_name , n ) {
  last_n_lines = list( [0:n] ) as { null }
  cur_inx = 0 
  lc = 0 
  for ( line : file(file_name) ){
    lc += 1 
    cur_inx %= n
    last_n_lines[cur_inx] = line 
    cur_inx += 1  
  }
  // print back the last_n_lines, imagining a circular buffer
  start_inx =  lc % n  
  
  for ( [start_inx:n] ){ (x = last_n_lines[$]) || x == null || println(x) }
  for ( [0:start_inx] ){ (x = last_n_lines[$]) || x == null || println(x) } 
}

tail_function( @ARGS[0] , @ARGS[1])