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Optimize Double.countPairs using frequency map #136

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Optimize Double.countPairs using frequency map #136

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20 changes: 11 additions & 9 deletions app/src/main/java/control/Double.java
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Original file line number Diff line number Diff line change
@@ -1,5 +1,8 @@
package control;

import java.util.HashMap;
import java.util.Map;

public class Double {
/**
* Sums all values squared from 0 to n
Expand Down Expand Up @@ -44,19 +47,18 @@ public static int sumTriangle(int n) {
* @return The number of pairs in the array.
*/
public static int countPairs(int[] arr) {
Map<Integer, Integer> frequencies = new HashMap<>();
for (int value : arr) {
frequencies.merge(value, 1, Integer::sum);
}

int count = 0;
for (int i = 0; i < arr.length; i++) {
int nDuplicates = 0;
for (int j = 0; j < arr.length; j++) {
if (arr[i] == arr[j]) {
nDuplicates++;
}
}
if (nDuplicates == 2) {
for (int frequency : frequencies.values()) {
if (frequency == 2) {
count++;
}
}
return count / 2;
return count;
}

/**
Expand Down