Disk File Sorting Programming

I started to look at programming. The first problem was the sorting of disks. I thought it was just merging and sorting, but the question required 1 MB of memory. This algorithm is not feasible. Programming Pearl writes to the use of Bitmap (two operations can be successfully achieved, less than 1 MB of memory). For details, see the first chapter of programming Pearl.

Question: give 10 ^ 7 data and sort big data. The memory size is only 1 MB, which is acceptable in a short time.

Solution: 1. Merge multiple channels. 2. Bitmap operations.

I read July's article here, and it's really good. Recommended: http://blog.csdn.net/v_JULY_v/article/details/6451990

A program that generates different random numbers is included below:

1 # include <iostream> 2 # include <time. h> 3 # include <assert. h> 4 using namespace STD; 5 6 const int size = 10000000; 7 int num [size]; 8 9 int main () 10 {11 int N; 12 file * fp = fopen ("data.txt", "W"); 13 assert (FP); 14 15 for (n = 1; n <= size; n ++) 16 // n = 0; n <size. As a result, the test data of a small program is 0, which is hereby corrected. 17 num [N] = N; 18 srand (unsigned) Time (null); 19 int I, j; 20 21 for (n = 0; n <size; N ++) 22 {23 I = (RAND () * rand_max + rand () % 10000000; 24 J = (RAND () * rand_max + rand () % 10000000; 25 swap (Num [I], num [J]); 26} 27 28 for (n = 0; n <size; n ++) 29 fprintf (FP, "% d", num [N]); 30 fclose (FP); 31 return 0; 32}

The bitmap program sorts the data by sorting the first 5000000 (each number corresponds to a bit) and the remaining 5000000 (each time it is smaller than 1 m). The Code is as follows (simulated twice ):

1 # include <iostream> 2 # include <bitset> 3 # include <assert. h> 4 # include <time. h> 5 using namespace STD; 6 7 const int max_each_scan = 5000000; 8 9 int main () 10 {11 clock_t begin = clock (); 12 bitset <max_each_scan> bit_map; 13 bit_map.reset (); 14 15 // open the file with the unsorted data 16 file * fp_unsort_file = fopen ("data.txt", "R"); 17 assert (fp_unsort_file ); 18 int num; 19 20 // The first Time scan to sort the data between 0-4999999 21 While (fscanf (fp_unsort_file, "% d", & num )! = EOF) 22 {23 if (Num <max_each_scan) 24 bit_map.set (Num, 1); 25} 26 27 file * fp_sort_file = fopen ("sort.txt", "W "); 28 assert (fp_sort_file); 29 int I; 30 31 // write the sorted data into file 32 for (I = 0; I <max_each_scan; I ++) 33 {34 if (bit_map [I] = 1) 35 fprintf (fp_sort_file, "% d", I ); 36} 37 38 // The second time scan to sort the data between 5000000-9999999 39 int result = fseek (F P_unsort_file, 0, seek_set); 40 if (result) 41 cout <"fseek failed! "<Endl; 42 else 43 {44 bit_map.reset (); 45 while (fscanf (fp_unsort_file," % d ", & num )! = EOF) 46 {47 If (Num> = max_each_scan & num <10000000) 48 {49 num-= max_each_scan; 50 bit_map.set (Num, 1 ); 51} 52} 53 for (I = 0; I <max_each_scan; I ++) 54 {55 if (bit_map [I] = 1) 56 fprintf (fp_sort_file, "% d", I + max_each_scan); 57} 58} 59 60 clock_t end = clock (); 61 cout <"bitmap method, time consumed:" <Endl; 62 cout <(end-begin)/clk_tck <"S" <Endl; 63 fclose (fp_sort_file); 64 fclose (fp_unsort_file); 65 return 0; 66}