[leetcode] Subsets

Subsets

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Question Solution 

Given a set of distinct integers, S, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If S = [1,2,3], a solution is:

[  [3],  [1],  [2],  [1,2,3],  [1,3],  [2,3],  [1,2],  []
]
package com.wyt.leetcodeOJ;import java.util.ArrayList;import java.util.Arrays;import java.util.List;/** * @author wangyitao * @Date 2015-01-08 * @version 1.0 * @AC Time 202ms */public class Subsets {public static void main(String[] args) {int[] S = {1,2};int max = 2>>1;System.out.println(max);System.out.println(7&1);List<List<Integer>> subsets = subsets(S);System.out.println(subsets);}public static List<List<Integer>> subsets(int[] S) {        List<List<Integer>> subsets = new ArrayList<List<Integer>>();        if (S != null) {                Arrays.sort(S);//子集有序，题目所需                int n = 1 << S.length;//子集个数为2^S.length                        for (int i = 0; i < n; i++) {            List<Integer> list = new ArrayList<Integer>();            int index = 0;            int j = i;            while (j > 0) {            if((j & 1) != 0) {//j的二进制形式，按位与1，为0表示该位置的元素没有如，101&1==1-->add(s0),index+1=s1,j>>1=10&1==0,s1不在，            list.add(S[index]);            }            index++;//标志前移            j = j >> 1;//j右移，一直到0            }    subsets.add(list);    }}                return subsets;    }}