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Cleanup combination and combination test (#5902)

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This commit is contained in:
Giulio Tantaro
2024-10-26 20:39:23 +02:00
committed by GitHub
parent b5a097c56a
commit e6f70634a4
2 changed files with 37 additions and 12 deletions
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27
src/main/java/com/thealgorithms/backtracking/Combination.java
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@ -1,6 +1,7 @@
package com.thealgorithms.backtracking;
import java.util.Arrays;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.TreeSet;
@ -13,8 +14,6 @@ public final class Combination {
private Combination() {
}
private static int length;
/**
* Find all combinations of given array using backtracking
* @param arr the array.
@ -23,39 +22,45 @@ public final class Combination {
* @return a list of all combinations of length n. If n == 0, return null.
*/
public static <T> List<TreeSet<T>> combination(T[] arr, int n) {
if (n == 0) {
return null;
if (n < 0) {
throw new IllegalArgumentException("The combination length cannot be negative.");
}
if (n == 0) {
return Collections.emptyList();
}
length = n;
T[] array = arr.clone();
Arrays.sort(array);
List<TreeSet<T>> result = new LinkedList<>();
backtracking(array, 0, new TreeSet<T>(), result);
backtracking(array, n, 0, new TreeSet<T>(), result);
return result;
}
/**
* Backtrack all possible combinations of a given array
* @param arr the array.
* @param n length of the combination
* @param index the starting index.
* @param currSet set that tracks current combination
* @param result the list contains all combination.
* @param <T> the type of elements in the array.
*/
private static <T> void backtracking(T[] arr, int index, TreeSet<T> currSet, List<TreeSet<T>> result) {
if (index + length - currSet.size() > arr.length) {
private static <T> void backtracking(T[] arr, int n, int index, TreeSet<T> currSet, List<TreeSet<T>> result) {
if (index + n - currSet.size() > arr.length) {
return;
}
if (length - 1 == currSet.size()) {
if (currSet.size() == n - 1) {
for (int i = index; i < arr.length; i++) {
currSet.add(arr[i]);
result.add((TreeSet<T>) currSet.clone());
result.add(new TreeSet<>(currSet));
currSet.remove(arr[i]);
}
return;
}
for (int i = index; i < arr.length; i++) {
currSet.add(arr[i]);
backtracking(arr, i + 1, currSet, result);
backtracking(arr, n, i + 1, currSet, result);
currSet.remove(arr[i]);
}
}