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Subsets.java

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import java.util.Arrays;

import java.util.LinkedList;

import java.util.List;

/**

* 思路是对每个index，有两种情况，要还是不要

* 要注意的是添加结果到result时，要复制一个列表，别直接加list

*/

public class Subsets {

/**

* 时间复杂度O(2^n)，空间复杂度 O(n)

*/

/**

public List<List<Integer>> subsets(int[] nums) {

List<List<Integer>> result = new LinkedList<List<Integer>>();

if (nums.length == 0) {

return result;

}

subsets(nums, 0, result, new LinkedList<Integer>());

return result;

}

private void subsets(int[] nums, int start, List<List<Integer>> list, List<Integer> path) {

if (start == nums.length) {

list.add(new LinkedList<Integer>(path));

return;

}

path.add(nums[start]);

subsets(nums, start + 1, list, path);

path.remove(path.size() - 1);

subsets(nums, start + 1, list, path);

}

*/

public List<List<Integer>> subsets(int[] nums) {

List<List<Integer>> result = new LinkedList<List<Integer>>();

if (nums.length == 0) {

return result;

}

Arrays.sort(nums);

subsets(nums, 0, result, new LinkedList<Integer>());

return result;

}

private void subsets(int[] nums, int start, List<List<Integer>> result, List<Integer> path) {

result.add(new LinkedList<Integer>(path));

for (int i = start; i < nums.length; i++) {

path.add(nums[i]);

subsets(nums, i + 1, result, path);

path.remove(path.size() - 1);

}

}

}