How to pick the max top 10 quantity from HashTable C++? - c++

Question

I already wrote a working project but my problem is, the last part.I have already Read 500.000 row from csv file into vector, then put into the hashtable.I can print whole hashtable but I need to pick top 10 Quantity from my hashtable.Just be clear, I am not about to sort the whole hashtable, just pick top 10.
The topic of my project is,program must be able to store individual products (given with StockCode) from csv file and insert it into a suitable data structure. If that product is already inserted into the structure, its counter must be increased by the quantity of the order.After reading and processing is over, your program must list the “top 10” products ordered by individuals.
There is rule about the libraries, This will be a proper C++ class. You must be able to create many instances of this class. (Please use no third party libraries and C++ STL, Boost etc.) However, you can use, iostream, ctime, fstream, string like IO and string classes.
Important note: Only thing I should focus is speed, storage or size is not a problem.
What I've done so far is,
Read Csv file row by row into vector
Stockcodes in row[1], Quantity in row[3]
Put them into Hashtable and increase their quantity by the quantity of the order.
Print the whole hash table.
What I need to do is,
Print the Top 10 Quantity
Now let's share Example csv file, Driver program codes, Output of the print function.
Csv File look like this:
InvoiceNo;StockCode;Description;Quantity;
536365;85123A;WHITE HANGING HEART T-LIGHT HOLDER;6
536365;71053;WHITE METAL LANTERN;6;
536365;84029G;KNITTED UNION FLAG HOT WATER BOTTLE;6;
536365;84029E;RED WOOLLY HOTTIE WHITE HEART.;6;
536365;22752;SET 7 BABUSHKA NESTING BOXES;2;
536365;21730;GLASS STAR FROSTED T-LIGHT HOLDER;6;
main.cpp
void printMaxQuantity() {
int maxValue=0;
for (int i = 0; i < 1000000; ++i) {
if(table[i] != nullptr) {
if (table[i]->quantity > maxValue)
maxValue = table[i]->quantity;
if (table[i]->quantity == maxValue) {
cout << "Index: " << i << endl;
cout << "StockCode: " << table[i]->stockCode << endl;
cout << "Quantity: " << table[i]->quantity << endl;
cout << endl << endl;
}
}
}
}
};
Here the output:(After edit the code StockCode: 85123A is correct output, but still struggling about the top 10)
Index: 41240
StockCode: 10002
Quantity: 48
Index: 309193
StockCode: 85123A
Quantity: 72
Process finished with exit code 0
Also one last note, I am doing this for a school project so I shouldn't use any third party software or include any different libraries because it is not allowed (I will implement my own vector class later)

Answer 1

Since this is homework, I will avoid writing actual code. Since you do not have any prior information about the actual data set, you will need to loop through it, which is a linear complexity. In order to find the top 10 items I advise you to create an array of 10 items to store the best items you get so far.
The first step is to copy the first 10 elements into your array.
The second step is sort your array of 10 items descendingly, so you will always use the last item for comparison.
Now you can loop the big structure and on each step, compare the current item with the last one of the array of ten elements. If it's lower, then do nothing. If it's higher, then find the highest ranked item in your array of 10 items which is smaller than the item you intend to insert due to higher quality. When you find that item, loop from the end until this item until your array of ten elements and on each step override the curret element with the current one. Finally override the now duplicate element.
Example: Assuming that your 7th element has lower quality than the one you intend to insert, but the 6th has higher quality override 9th element with the 8th, then the 8th with the 7th and then the 7th with the item you just found. Remember that array indexes start from 0.

Answer 2

This is what you want clearly.This code pick the top 10 from your hash table
void hashTable::printTopTen() {
int maxValue = 0;
int indexHolder = 0;
cout << "#" << " " << "Stock Code" << "\t" << "Description" << "\t\t\t" << "Quantity" << endl;
for (int i = 0; i < 10; ++i) { //-> This loop for top 10
for (int index = 0; index < TABLE_SIZE; ++index) { //-> base loop to find max quantity in hash table
if (table[index] != nullptr) { // to check if index is NULL or not
if (table[index]->quantity > maxValue) {
maxValue = table[index]->quantity; //update the maxValue with biggest quantity
indexHolder = index; // -> to store index number of max quantity in hash table
}
}
}
for (int indeX = 0; indeX < TABLE_SIZE; ++indeX) { //find the max quantity's stockCode,description
if (table[indeX] != nullptr) { // to check if index is NULL or not
if (table[indeX]->quantity == maxValue) { //if we have reached the maxValue then it's quantity is top 1
cout << i + 1 << "." << " " << table[indeX]->stockCode << "\t" << table[indeX]->description
<< "\t" << table[indeX]->quantity << endl;
table[indexHolder]->quantity = 0; //after cout the max one, delete the index so it can't be top 1 again
}
}
}
maxValue = 0; // update max value 0 again for second base loop
}
}

Answer 3

This question already has an answer. But I want to show you how to perform selection sort so you can compare it with your code.
**Performance trick: ** Quick Sort algorithm can be used instead of Selection Sort
hashMap=hashTable, hashEntry=Node, so this what I did:
void hashTable::selectionSort() {
int firstCounter, secondCounter;
Node *emptyOne = new Node("empty", "thisEmpty", 0);
Node *temp;
for (firstCounter = 1; firstCounter < TABLE_SIZE; firstCounter++) {
if (table[firstCounter] == nullptr) {
table[firstCounter] = emptyOne;
}
temp = table[firstCounter];
secondCounter = firstCounter - 1;
if (table[secondCounter] == nullptr) {
table[secondCounter] = emptyOne;
}
while (secondCounter >= 0 && table[secondCounter]->quantity > temp->quantity) {
table[secondCounter + 1] = table[secondCounter];
secondCounter = secondCounter - 1;
if (table[secondCounter] == nullptr) {
table[secondCounter] = emptyOne;
}
}
table[secondCounter + 1] = temp;
}
}