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findPairs.java

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package Arrays;

import java.util.HashMap;

import java.util.HashSet;

import java.util.Map;

import java.util.Set;

public class findPairs {

/**

* Given an array find those pairs whose sum is equal to n

* @param arr

* @param sum

*/

public static void findPairs(int [] arr, int sum){

Set<Integer> s = new HashSet<>();

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

int complement = sum - arr[i];

if(s.contains(complement)){

System.out.println("Pair found: "+arr[i]+ ","+complement);

}

s.add(arr[i]);

}

}

public static void findPairsusingHashmap(int [] arr, int sum){

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

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

int complement = sum - arr[i];

if (map.containsKey(complement)) {

int count = map.get(complement);

System.out.println("Pair found: " + arr[i] + "," + complement + " (Count: " + count + ")");

}

map.put(arr[i], map.getOrDefault(arr[i], 0) + 1);

}

}

public static void main(String [] args){

int [] arr = {3, 4, 1, 2, 5, 7, 8};

int sum = 9;

findPairs(arr,sum);

findPairsusingHashmap(arr,sum);

}

}