[LeetCode] 47. Permutations II

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]
]

Thought process:
If the collection contains duplicate, I cannot only use the original method I used in "46. Permutations", because it will produce duplicate permutations. For example, if the collection is [0, 1, 1], the result will contain two [0, 1, 1]s.
The idea is to maintain a rule about which one of the duplicate numbers can appear in the permutations. To do this, I can sort the array and make sure that only the number with a smaller index can appear in a duplicate permutation.
For example, as I add numbers to the permutation list, if I found that I'm adding the second 1 while the first 1 is not in the list, that means the first 1 has already been used to make the exact same permutation. So I continue to the next iteration.

Solution:
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
public class Solution {
    public List<List<Integer>> permuteUnique(int[] nums) {
        List<List<Integer>> permutations = new ArrayList<>();
        List<Integer> permutation = new ArrayList<>();
        boolean[] visited = new boolean[nums.length];
        Arrays.sort(nums);
        permuteUnique(nums, permutation, visited, permutations);
        
        return permutations;
    }
    
    private void permuteUnique(int[] nums, List<Integer> permutation, boolean[] visited, List<List<Integer>> permutations) {
        if (permutation.size() == nums.length) {
            permutations.add(new ArrayList<>(permutation));
        }
        
        for (int i = 0; i < nums.length; i++) {
            if (visited[i] || (i > 0 && nums[i] == nums[i - 1] && !visited[i - 1])) {
                continue;
            }
            
            visited[i] = true;
            permutation.add(nums[i]);
            permuteUnique(nums, permutation, visited, permutations);
            permutation.remove(permutation.size() - 1);
            visited[i] = false;
        }
    }
}

Time complexity: O(n! * n).
Location: San Jose, CA, USA

Comments

  1. Eman QurashiDecember 25, 2021 at 2:22 AM

    Popular Solution Leetcode 46/47
    I found that solution is very popular and helpful: https://youtu.be/UvSPsz0jTQ4

    ReplyDelete

Post a Comment

Popular posts from this blog

[LeetCode] 631. Design Excel Sum Formula

Your task is to design the basic function of Excel and implement the function of sum formula. Specifically, you need to implement the following functions: Excel(int H, char W):  This is the constructor. The inputs represents the height and width of the Excel form.  H  is a positive integer, range from 1 to 26. It represents the height.  W  is a character range from 'A' to 'Z'. It represents that the width is the number of characters from 'A' to  W . The Excel form content is represented by a height * width 2D integer array  C , it should be initialized to zero. You should assume that the first row of  C  starts from 1, and the first column of  C  starts from 'A'. void Set(int row, char column, int val):  Change the value at  C(row, column)  to be val. int Get(int row, char column):  Return the value at  C(row, column) . int Sum(int row, char column, List of Strings : numbers):  This function calculate and set the value at  C(row, column) , wh
Read more

[LeetCode] 269. Alien Dictionary

There is a new alien language which uses the latin alphabet. However, the order among letters are unknown to you. You receive a list of  non-empty  words from the dictionary, where  words are sorted lexicographically by the rules of this new language . Derive the order of letters in this language. Example 1: Given the following words in dictionary, [ "wrt", "wrf", "er", "ett", "rftt" ] The correct order is:  "wertf" . Example 2: Given the following words in dictionary, [ "z", "x" ] The correct order is:  "zx" . Example 3: Given the following words in dictionary, [ "z", "x", "z" ] The order is invalid, so return  "" . Note: You may assume all letters are in lowercase. You may assume that if a is a prefix of b, then a must appear before b in the given dictionary. If the order is invalid, return an empty string
Read more

[LeetCode] 714. Best Time to Buy and Sell Stock with Transaction Fee

Your are given an array of integers  prices , for which the  i -th element is the price of a given stock on day  i ; and a non-negative integer  fee  representing a transaction fee. You may complete as many transactions as you like, but you need to pay the transaction fee for each transaction. You may not buy more than 1 share of a stock at a time (ie. you must sell the stock share before you buy again.) Return the maximum profit you can make. Example 1: Input: prices = [1, 3, 2, 8, 4, 9], fee = 2 Output: 8 Explanation: The maximum profit can be achieved by: Buying at prices[0] = 1 Selling at prices[3] = 8 Buying at prices[4] = 4 Selling at prices[5] = 9 The total profit is ((8 - 1) - 2) + ((9 - 4) - 2) = 8. Note: 0 < prices.length <= 50000 . 0 < prices[i] < 50000 . 0 <= fee < 50000 . Thought process: Each day there are two options, buy or sell. Use two variables buy and sell to keep track of the max profit. Solution: 1 2 3 4 5 6
Read more