LeetCode 47. Permutations II (full array II)

Topic Tags: Backtracking

　　DFS use, to establish a tempList, was added to each recursive digital, using boolean [] used to skip numbers used, and skip duplicate combinations.

　　Specifically to see code.

  

Java Solution: 

Runtime:  1 ms, faster than 99.60 % 

Memory Usage: 41.7 MB, less than 11.94 %

Completion Date: 11/08/2019

The key points: the establishment of boolean [] used

class Solution {
    
    List<List<Integer>> res;
    
    public List<List<Integer>> permuteUnique(int[] nums) {
        res = new ArrayList<>();
        List<Integer> tempList = new ArrayList<>();
        boolean[] used = new boolean[nums.length];
        Arrays.sort(nums);
        DFS(nums, tempList, used);
        
        return res;
    }
    
    private void DFS(int[] nums, List<Integer> tempList, boolean[] used) {
        if(tempList.size() == nums.length) {
            res.add(new ArrayList<>(tempList));
            return;
        }

        for(int i=0 ; i<nums.length; i++) {
            if(used[i])
                continue;
            if(i>0 && nums[i-1] == nums[i] && !used[i-1]) // if it is a duplicated permutation, skip
                continue;

            used[i] = true;
            tempList.add(nums[i]);
            DFS(nums, tempList, used);
            used[i] = false;
            tempList.remove(tempList.size() - 1);
            
        }
    }
}

References: n / a

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