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package com.yangchd.leetcode.medium;

import java.util.ArrayList;

import java.util.List;

/**

* @author yangchd 2018/11/7.

*

* 78.Subsets

* Given a set of distinct integers, nums, return all possible subsets (the power set).

*

* Note: The solution set must not contain duplicate subsets.

*

* Example:

* Input: nums = [1,2,3]

* Output:

* [

* [3],

* [1],

* [2],

* [1,2,3],

* [1,3],

* [2,3],

* [1,2],

* []

* ]

*

*/

public class Subsets {

/**

* 这种获取所有子集的问题，拆分成所有包含n个子集的问题

* 然后用回溯算法，得到包含n个子集的所有可能解

*/

class Solution {

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

List<List<Integer>> res = new ArrayList<List<Integer>>();

for (int i = 0; i <= nums.length; i++) {

backTracking(res, new ArrayList<Integer>(), 0, i, nums);

}

return res;

}

private void backTracking(List<List<Integer>> res, List<Integer> list, int begin, int k, int[] nums) {

if (list.size() == k) {

res.add(new ArrayList<Integer>(list));

} else {

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

list.add(nums[i]);

backTracking(res, list, i + 1, k, nums);

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

}

}

}

}

}