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[leetcode] Subsets II

Given a collection of integers that might contain duplicates, S, return all possible subsets.

Note:

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

https://oj.leetcode.com/problems/subsets-ii/

 

思路:关键是去重,先排序,然后根据后一个是否跟前一个相等来判断是否继续递归。

import java.util.ArrayList;import java.util.Arrays;public class Solution {    public ArrayList<ArrayList<Integer>> subsetsWithDup(int[] num) {        ArrayList<ArrayList<Integer>> ans = new ArrayList<ArrayList<Integer>>();        ArrayList<Integer> tmp = new ArrayList<Integer>();        // sort first        Arrays.sort(num);        sub(num, 0, tmp, ans);        return ans;    }    public void sub(int[] num, int k, ArrayList<Integer> tmp, ArrayList<ArrayList<Integer>> ans) {        ArrayList<Integer> arr = new ArrayList<Integer>(tmp);        ans.add(arr);        for (int i = k; i < num.length; i++) {            // remove the dup            if (i != k && num[i] == num[i - 1])                continue;            tmp.add(num[i]);            sub(num, i + 1, tmp, ans);            tmp.remove(tmp.size() - 1);        }    }    public static void main(String[] args) {        System.out.println(new Solution().subsetsWithDup(new int[] { 1, 2, 2 }));    }}
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参考:

http://www.cnblogs.com/lautsie/p/3249869.html