Question

import java.util.*;

public class PairFinder {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
  
// Read in the value of k
int k = Integer.parseInt(sc.nextLine());
  
// Read in the list of numbers
int[] numbers;
String input = sc.nextLine();
if (input.equals("")) {
numbers = new int[0];
} else {
String[] numberStrings = input.split(" ");
numbers = new int[numberStrings.length];
for (int i = 0; i < numberStrings.length; i++) {
numbers[i] = Integer.parseInt(numberStrings[i]);
}
}
  
System.out.println(findPairs(numbers, k));
}
  
//method that tells you number of pairs that add to int k
private static int findPairs(int[] numbers, int k) {
// Tracks the number of pairs found
int pairsFound = 0;
int dulipcates = 0;
//initializing the HashMaps
Map<Integer, Integer> pairs = new HashMap<Integer, Integer>();
//initializing the ArrayList
List<Integer> numbersCopy = new ArrayList<>();
  
//copying the numbers into an ArrayList
for(int i=0; i<numbers.length; i++){
numbersCopy.add(numbers[i]);
}
  
//adding all the numbers from the array into a HashMap object
for(int i = 0; i<numbers.length; i++){
  
// making the otherPair into the key for HashMap
int otherPair = k - (numbers[i]);

  

if(numbersCopy.contains(otherPair)){


  
  

  
if(Collections.frequency(numbersCopy, otherPair) > 0){
//pairs.remove(numbersCopy.get(otherPair));
numbersCopy.remove(otherPair);
dulipcates = Collections.frequency(numbersCopy, otherPair);
  
}else{

pairs.put(otherPair, numbersCopy.get(i));
pairsFound++;
  
}
  
  
  
  
}
  
}
  
return (pairsFound+dulipcates);
}

}

This is my code and I'm not sure why its not returning correcting. I must also count the duplicates in the array.

In this problem we will write a program that, given an integer k and a list of integers, outputs the number of pairs in in the list that add to k. To receive full credit for design, your algorithm must have a runtime in O(n), where n is the length of the list of integers. Your program should take as input a number k on its own line, followed by a space-separated list of integers. It should then output the number of pairs in the list that add to k. Order does not matter when considering a pair (in other words, in the list 2,1] there is one distinct pair that sums to 3, not two. You may not assume that all numbers in the input are distinct For example, if our file input.txt is: 12 34 -2 -3 -3 then we should print: since there are three pairs that sum to 1: 3+(-2) and 4+(-3) twice (one for each -3). As another example, if input.txt is: 1122 then we should print since there are 4 possible pairings of a 1 and a 2 in this list

Answer 1

import java.util.*;

public class PairFinder {

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

// Read in the value of k

int k = Integer.parseInt(sc.nextLine());

// Read in the list of numbers

int[] numbers;

String input = sc.nextLine();

if (input.equals("")) {

numbers = new int[0];

} else {

String[] numberStrings = input.split(" ");

numbers = new int[numberStrings.length];

for (int i = 0; i < numberStrings.length; i++) {

numbers[i] = Integer.parseInt(numberStrings[i]);

}

}

System.out.println(findPairs(numbers, k));

}

// method that tells you number of pairs that add to int k

private static int findPairs(int[] numbers, int k) {

// Tracks the number of pairs found

int pairsFound = 0;

int dulipcates = 0;

// initializing the HashMaps

Map<Integer, Integer> pairs = new HashMap<Integer, Integer>();

for (int i=0; i<numbers.length; i++){

  

if(!pairs.containsKey(numbers[i]))

pairs.put(numbers[i],0);

  

pairs.put(numbers[i], pairs.get(numbers[i])+1);

}

for (int i=0; i<numbers.length; i++)

{

if(pairs.get(k-numbers[i]) != null)

pairsFound += pairs.get(k-numbers[i]);

if (k-numbers[i] == numbers[i])

pairsFound--;

}

  

return pairsFound/2;

}

}

==============================================================
See OUTPUT

10 int k-Integer.parseInt(sc.nextLineO); 12 13 14 15 16 17 18 19 20 21 //Read in the list of numbers intI numbers; String input sc.nextLine; if (input.equals("") I numbersnew int[0]; } else String] numberStringsinput.split(" "); numbersnew int[numberStrings.length]; for (inti- 0; i < numberStrings.length; i++) 1 numbers [i] = Integer.parseInt(numberStrings[i]); 23 24 25 26 27 28 29e 30 31 32 System.out.println(findPairs(numbers, k)); /7method that tells you number of pairs that add to int k private static int findPairs(int numbers, int k) I // Tracks the number of pairs found int pairsFound0; int dulipcates0; // initializing the HashMaps Map<Integer, Integer» pairs-new HashMap<Integer, Integer»(); 34 35 36 for (int i-0; i<numbers.length; i++)I Console 3 <terminated> PairFinder [Java Application] /Library/Java/JavaVirtualMachinesljdk1.8.0_202.jdk/Contents/Home 1 1 2 2


Thanks, PLEASE COMMENT if there is any concern.