A review and extension of cs132:sort a file with 120 records. However, due to memory restrictions only 20 records may be placed into memory. You are to implement a quasi external sort

CODE/DIRECTIONS:

For the sake of simplicity, and without much loss of generality, we will say for this lab are records are just ints : thus sort a file with 120 ints where only 20 ints maybe placed into memory at any one time

general idea:

break data into blocks, sort blocks into runs, merge runs

less general idea:

Call inFile1 our source file ( the one with the initial 120 records to be sorted. You will also need an inFile2, and 2 other files outFile1 and outFile2.

Break the file into blocks of size 20: in this case there will be 6 blocks ( 120/20 ) Sort the blocks by

read a block, sort it, store in outFile1

read a block, sort it, store in outFile2

read a block, sort it, store in outFile1

( in other words, sort a block and alternately place in the files outFile1, outFile2 )

By definition a run is a sorted block

Note that each file outFile1 and outFile2 will have half of the runs Merge the runs

Merge data from outFile1 and outFile2 to inFile1 and inFile2.

Merge the first run on outFile1 and the first run on outFile2,

and store the result on inFile1:

Read two records in main memory, compare, store the smaller

on inFile1

Read the next record from either outFile1 or outFile2 the file

that had its record moved/stored to inFile1

Similarly merge the second run on outFile1 and the second run on outFile2, store the result on inFile2.

Merge the third run on outFile1 and the third run on outFile2, store

the result on inFile1... etc

merging each run and storing the result alternatively on inFile1 and inFile2.

At the end

inFile1 and inFile2 will contain sorted runs twice the size of the previous runs on outFile1 and outFile2

Now merge data from inFile1 and inFile2 to outFile1 and outFile2.

Merge the first run on inFile1 and the first run on inFile2, and store

the result on outFile1.

Merge the second run on inFile1 and the second run on inFile2, store the result on outFile2

Etc, merge and store alternatively on inFile1 and inFile2.

Repeat the process until only one run is obtained. This would be the sorted file

Must use above algorithm