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Problem78_subsets.java
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package com.longluo.top100;
import com.longluo.datastructure.ArrayUtils;
import java.util.ArrayList;
import java.util.List;
/**
* 78. 子集
* <p>
* 给你一个整数数组 nums ，数组中的元素 互不相同 。返回该数组所有可能的子集（幂集）。
* 解集 不能 包含重复的子集。你可以按 任意顺序 返回解集。
* <p>
* 示例 1：
* 输入：nums = [1,2,3]
* 输出：[[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3]]
* <p>
* 示例 2：
* 输入：nums = [0]
* 输出：[[],[0]]
* <p>
* 提示：
* 1 <= nums.length <= 10
* -10 <= nums[i] <= 10
* nums 中的所有元素 互不相同
* <p>
* https://leetcode.com/problems/subsets/
*/
public class Problem78_subsets {
// Backtrack time: O(2^n) space: O(n)
public static List<List<Integer>> subsets(int[] nums) {
if (nums == null || nums.length == 0) {
return new ArrayList<>();
}
List<List<Integer>> ans = new ArrayList<>();
backtrack(ans, new ArrayList<>(), nums, 0);
return ans;
}
public static void backtrack(List<List<Integer>> ans, List<Integer> oneList, int[] numbers, int index) {
if (index == numbers.length) {
ans.add(new ArrayList<>(oneList));
return;
}
oneList.add(numbers[index]);
backtrack(ans, oneList, numbers, index + 1);
oneList.remove(oneList.size() - 1);
backtrack(ans, oneList, numbers, index + 1);
}
public static void main(String[] args) {
System.out.println("[[],[1],[1,2],[1,2,2],[2],[2,2]] ?= " + ArrayUtils.print2DList(subsets(new int[]{1, 2, 2})));
System.out.println("[[],[0]] ?= " + ArrayUtils.print2DList(subsets(new int[]{0})));
}
}