CareerCup

public class TopNEntriesFromFiles {
	
	/**
	 * Read given files and find top n customers by expenses.
	 * Assume that file format is comma separated values:  
	 * customer_id, product_id, expenses
	 * (e.g. 1,32,5564)
	 * @param n 
	 * 		number of map entries to return
	 * @param paths 
	 * 		files to process
	 * @return top n entries from given files
	 */
	private static Map<Integer, Integer> processFiles(int n, String... paths) {
		Map<Integer, Integer> temp = new LinkedHashMap<>();
		Map<Integer, Integer> result = new LinkedHashMap<>();
		for (String path : paths) {
			try (BufferedReader br = new BufferedReader(new FileReader(path))) {
				String line = br.readLine();
				while (line != null) {
					int customerId = Integer.parseInt(line.split(",")[0]);
					int expences = Integer.parseInt(line.split(",")[2]);
					if (temp.containsKey(customerId)) {
						temp.put(customerId, temp.get(customerId) + expences);
					} else {
						temp.put(customerId, expences);
					}
					line = br.readLine();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
		List<Integer> sortedKeys = sortMap(temp);
		for (Integer key : sortedKeys.subList(sortedKeys.size() - n, sortedKeys.size())) {
			result.put(key, temp.get(key));
		}
		return result;
	}
	
	/**
	 * Test
	 * @param args 
	 * 		paths to files
	 */
	public static void main(String[] args) {
		Map<Integer, Integer> m = processFiles(5, args);
		for (Integer k : m.keySet()) {
			System.out.println("customer_id: " + k + "\t expenses: " + m.get(k));
		}
	}
	
	/**
	 * Sort map by values
	 * @param map
	 * 		unsorted map
	 * @return map sorted by values
	 */
	private static List<Integer> sortMap(final Map<Integer, Integer> map) {
	    Set<Integer> set = map.keySet();
	    List<Integer> keys = new ArrayList<Integer>(set);
	    Collections.sort(keys, new Comparator<Integer>() {
	        @Override
	        public int compare(Integer i1, Integer i2) {
	            return map.get(i1) - map.get(i2);
	        }
	    });
	    return keys;
	}
}

Create a max heap of size 5. Read the elements from the file and put it in to heap. finally u will be left with max 5 values

Public class StaticM {



public static List<File> filesInDirectory(String sDirectory){

List<File> listFiles = new ArrayList<>();

File file = new File(sDirectory);

for(File file1: Arrays.asList(file.listFiles())){
if(file1.isDirectory()){
filesInDirectory(file1.toString());
}
else{
listFiles.add(file1);
}
}


return listFiles;
}


public static Map<String, Integer> FindMostExpCust() throws IOException{

MultiValueMap custExp = new MultiValueMap();
// keep all your files in temp directory
for(File file:StaticM.filesInDirectory("C:\\temp")){

FileReader reader = new FileReader(file);
BufferedReader bufRead = new BufferedReader(reader);
String line = "";
while((line=bufRead.readLine())!=null){
// CustomerID=12345, ProductID=456, Expenses=3200
custExp.put(line.split(",")[0].split("=")[1], Integer.parseInt(line.split(",")[2].split("=")[1]));
}

}

Map<String, Integer> mp1 = new HashMap<>();
int value=0;
Iterator<?> it = custExp.keySet().iterator();
while(it.hasNext()){
String key = (String) it.next();
for(int i=0;i<custExp.getCollection(key).toArray().length;i++){
value+=(int)custExp.getCollection(key).toArray()[i];
}
mp1.put(key, value);
}
return mp1;
}


public static void SortMap(Map<String,Integer> map){

List<?> list = new LinkedList(map.entrySet());
Collections.sort(list, new Comparator<Object>(){
public int compare(Object o1, Object o2){
return ((Comparable) ((Map.Entry) (o1)).getValue())
.compareTo(((Map.Entry) (o2)).getValue());
}
});
HashMap sortedHashMap = new LinkedHashMap();
for (Iterator it = list.iterator(); it.hasNext();) {
Map.Entry entry = (Map.Entry) it.next();
sortedHashMap.put(entry.getKey(), entry.getValue());
}

System.out.println(sortedHashMap);

}

public static void main(String[]args) throws IOException{

StaticM.SortMap(StaticM.FindMostExpCust());

}

}

public class StaticM {



public static List<File> filesInDirectory(String sDirectory){

List<File> listFiles = new ArrayList<>();

File file = new File(sDirectory);

for(File file1: Arrays.asList(file.listFiles())){
if(file1.isDirectory()){
filesInDirectory(file1.toString());
}
else{
listFiles.add(file1);
}
}


return listFiles;
}


public static Map<String, Integer> FindMostExpCust() throws IOException{

MultiValueMap custExp = new MultiValueMap();
// keep all your files in temp directory
for(File file:StaticM.filesInDirectory("C:\\temp")){

FileReader reader = new FileReader(file);
BufferedReader bufRead = new BufferedReader(reader);
String line = "";
while((line=bufRead.readLine())!=null){
// CustomerID=12345, ProductID=456, Expenses=3200
custExp.put(line.split(",")[0].split("=")[1], Integer.parseInt(line.split(",")[2].split("=")[1]));
}

}

Map<String, Integer> mp1 = new HashMap<>();
int value=0;
Iterator<?> it = custExp.keySet().iterator();
while(it.hasNext()){
String key = (String) it.next();
for(int i=0;i<custExp.getCollection(key).toArray().length;i++){
value+=(int)custExp.getCollection(key).toArray()[i];
}
mp1.put(key, value);
}
return mp1;
}


public static void SortMap(Map<String,Integer> map){

List<?> list = new LinkedList(map.entrySet());
Collections.sort(list, new Comparator<Object>(){
public int compare(Object o1, Object o2){
return ((Comparable) ((Map.Entry) (o1)).getValue())
.compareTo(((Map.Entry) (o2)).getValue());
}
});
HashMap sortedHashMap = new LinkedHashMap();
for (Iterator it = list.iterator(); it.hasNext();) {
Map.Entry entry = (Map.Entry) it.next();
sortedHashMap.put(entry.getKey(), entry.getValue());
}

System.out.println(sortedHashMap);

}

public static void main(String[]args) throws IOException{

StaticM.SortMap(StaticM.FindMostExpCust());

}

}

public class StaticM {



public static List<File> filesInDirectory(String sDirectory){

List<File> listFiles = new ArrayList<>();

File file = new File(sDirectory);

for(File file1: Arrays.asList(file.listFiles())){
if(file1.isDirectory()){
filesInDirectory(file1.toString());
}
else{
listFiles.add(file1);
}
}


return listFiles;
}


public static Map<String, Integer> FindMostExpCust() throws IOException{

MultiValueMap custExp = new MultiValueMap();
// keep all your files in temp directory
for(File file:StaticM.filesInDirectory("C:\\temp")){

FileReader reader = new FileReader(file);
BufferedReader bufRead = new BufferedReader(reader);
String line = "";
while((line=bufRead.readLine())!=null){
// CustomerID=12345, ProductID=456, Expenses=3200
custExp.put(line.split(",")[0].split("=")[1], Integer.parseInt(line.split(",")[2].split("=")[1]));
}

}

Map<String, Integer> mp1 = new HashMap<>();
int value=0;
Iterator<?> it = custExp.keySet().iterator();
while(it.hasNext()){
String key = (String) it.next();
for(int i=0;i<custExp.getCollection(key).toArray().length;i++){
value+=(int)custExp.getCollection(key).toArray()[i];
}
mp1.put(key, value);
}
return mp1;
}


public static void SortMap(Map<String,Integer> map){

List<?> list = new LinkedList(map.entrySet());
Collections.sort(list, new Comparator<Object>(){
public int compare(Object o1, Object o2){
return ((Comparable) ((Map.Entry) (o1)).getValue())
.compareTo(((Map.Entry) (o2)).getValue());
}
});
HashMap sortedHashMap = new LinkedHashMap();
for (Iterator it = list.iterator(); it.hasNext();) {
Map.Entry entry = (Map.Entry) it.next();
sortedHashMap.put(entry.getKey(), entry.getValue());
}

System.out.println(sortedHashMap);

}

public static void main(String[]args) throws IOException{

StaticM.SortMap(StaticM.FindMostExpCust());

}

}

Use threads with volatile keyword,
Each file will have its own hashmap, product id as key
Create thread for each file.
Increment volatile variable with each customer find.