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subsets.java
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94 lines (87 loc) · 2.52 KB
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// Source : https://oj.leetcode.com/problems/subsets/
// Inspired by : http://www.jiuzhang.com/solutions/subsets/
// Author : Lei Cao
// Date : 2015-10-02
/**********************************************************************************
*
* 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 subsets;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class subsets {
/**
* Leetcode version
* @param nums
* @return
*/
public List<List<Integer>> subsets(int [] nums) {
List<List<Integer>> result = new ArrayList<List<Integer>>();
if (nums == null || nums.length == 0) {
return result;
}
ArrayList<Integer> list = new ArrayList<Integer>();
Arrays.sort(nums);
addSubset(result, list, nums, 0);
return result;
}
private void addSubset(List<List<Integer>> result, ArrayList<Integer> list, int[] nums, int pos) {
result.add(new ArrayList<Integer>(list));
for (int i = pos; i < nums.length; i++) {
list.add(nums[i]);
addSubset(result, list, nums, i + 1);
list.remove(list.size()-1);
}
}
/**
* Lintcode version
* @param S: A set of numbers.
* @return: A list of lists. All valid subsets.
*/
public ArrayList<ArrayList<Integer>> subsets(ArrayList<Integer> s) {
// write your code here
ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
if (s == null || s.size() == 0) {
return result;
}
ArrayList<Integer> list = new ArrayList<Integer>();
Collections.sort(s);
addSubset(s, result, list, 0);
return result;
}
private void addSubset(
ArrayList<Integer> s,
ArrayList<ArrayList<Integer>> result,
ArrayList<Integer> list,
int pos) {
result.add(new ArrayList<Integer>(list));
for (int i = pos; i < s.size(); i++) {
list.add(s.get(i));
addSubset(s, result, list, i + 1);
list.remove(list.size() - 1);
}
}
}