【LeetCode】C# 47、Permutations II

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Given a collection of numbers that might contain duplicates, return all possible unique permutations.

For example,
[1,1,2] have the following unique permutations:
[
[1,1,2],
[1,2,1],
[2,1,1]
]
包含重复数的排列组合问题。

思路与上一题一样，关键在于利用
if(i>0 &&nums[i-1]==nums[i] && !used[i-1]) continue;
来跳过重复数的递归。

public class Solution {    public List<List<int>> PermuteUnique(int[] nums) {        List<List<int>> res = new List<List<int>>();        if(nums==null || nums.Length==0) return res;        bool[] used = new bool[nums.Length];        List<int> list = new List<int>();        Array.Sort(nums);        dfs(nums, used, list, res);        return res;    }    public void dfs(int[] nums, bool[] used, List<int> list, List<List<int>> res){        if(list.Count()==nums.Length){            res.Add(new List<int>(list));            return;        }        for(int i=0;i<nums.Length;i++){            if(used[i]) continue;            if(i>0 &&nums[i-1]==nums[i] && !used[i-1]) continue;            used[i]=true;            list.Add(nums[i]);            dfs(nums,used,list,res);            used[i]=false;            list.RemoveAt(list.Count()-1);        }    }}

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