leetcode 47. Permutations II
2017-06-26 18:29
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Given a collection of numbers that might contain duplicates, return all possible unique permutations.
For example,
For example,
[1,1,2]have the following unique permutations:
[ [1,1,2], [1,2,1], [2,1,1] ]
还是全排列问题,这次有重复数字,是一个通用解法,每次递归要看该数字是否是重复数字,如果是的话,前一个数字有没有被使用,使用了则可以递归,没有使用的话,该数字也要跳过。
public class Solution { public List<List<Integer>> permuteUnique(int[] nums) { List<List<Integer>> res = new ArrayList<List<Integer>>(); if(nums.length==0){ return res; } Arrays.sort(nums); List<Integer> item = new ArrayList<Integer>(); boolean []use = new boolean[nums.length]; helper(nums,res,item,use); return res; } public void helper(int[]nums,List<List<Integer>>res,List<Integer>item,boolean[]use){ if(item.size()==nums.length){ res.add(new ArrayList<Integer>(item)); return ; } for(int i=0;i<nums.length;i++){ if(i>0&&!use[i-1]&&nums[i-1]==nums[i])continue; if(!use[i]){ use[i]=true; item.add(nums[i]); helper(nums,res,item,use); item.remove(item.size()-1); use[i]=false; } } } }
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