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3835c4822a
### Summary This PR makes small readability and maintainability improvements to the algorithm implementation. ### Changes - Removed a redundant `n < 0` validation check since the method contract already ensures valid `n` - Replaced `current.remove(current.size() - 1)` with `current.removeLast()` to better express backtracking intent ### Rationale - Simplifies input validation without changing behavior - Uses the `Deque` API to make the backtracking step clearer and less error-prone ### Impact - No change in algorithm logic or time/space complexity - Output remains identical Co-authored-by: Swati Vusurumarthi <swativs869@gmail.com>
55 lines
1.9 KiB
Java
55 lines
1.9 KiB
Java
package com.thealgorithms.backtracking;
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import java.util.ArrayList;
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import java.util.List;
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/**
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* This class provides methods to find all combinations of integers from 0 to n-1
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* of a specified length k using backtracking.
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*/
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public final class ArrayCombination {
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private ArrayCombination() {
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}
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/**
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* Generates all possible combinations of length k from the integers 0 to n-1.
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*
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* @param n The total number of elements (0 to n-1).
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* @param k The desired length of each combination.
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* @return A list containing all combinations of length k.
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* @throws IllegalArgumentException if n or k are negative, or if k is greater than n.
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*/
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public static List<List<Integer>> combination(int n, int k) {
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if (k < 0 || k > n) {
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throw new IllegalArgumentException("Invalid input: 0 ≤ k ≤ n is required.");
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}
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List<List<Integer>> combinations = new ArrayList<>();
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combine(combinations, new ArrayList<>(), 0, n, k);
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return combinations;
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}
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/**
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* A helper method that uses backtracking to find combinations.
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*
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* @param combinations The list to store all valid combinations found.
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* @param current The current combination being built.
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* @param start The starting index for the current recursion.
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* @param n The total number of elements (0 to n-1).
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* @param k The desired length of each combination.
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*/
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private static void combine(List<List<Integer>> combinations, List<Integer> current, int start, int n, int k) {
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// Base case: combination found
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if (current.size() == k) {
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combinations.add(new ArrayList<>(current));
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return;
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}
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for (int i = start; i < n; i++) {
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current.add(i);
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combine(combinations, current, i + 1, n, k);
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current.removeLast(); // Backtrack
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}
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}
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}
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