[LeetCode] 384. Shuffle an Array 数组洗牌

Posted 2021-01-10 轻风舞动

Shuffle a set of numbers without duplicates.

Example:

// Init an array with set 1, 2, and 3.
int[] nums = {1,2,3};
Solution solution = new Solution(nums);

// Shuffle the array [1,2,3] and return its result. Any permutation of [1,2,3] must equally likely to be returned.
solution.shuffle();

// Resets the array back to its original configuration [1,2,3].
solution.reset();

// Returns the random shuffling of array [1,2,3].
solution.shuffle();

给一个没有重复数字的数组，实现重置和洗牌的功能。

解法：遍历数组每个位置，每次都随机生成一个坐标位置，然后交换当前位置和随机位置的数字，这样如果数组有n个数字，那么也随机交换了n组位置，从而达到了洗牌的目的。

Java:

import java.util.Random;

public class Solution {
    private int[] nums;
    private Random random;

    public Solution(int[] nums) {
        this.nums = nums;
        random = new Random();
    }
    
    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        return nums;
    }
    
    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        if(nums == null) return null;
        int[] a = nums.clone();
        for(int j = 1; j < a.length; j++) {
            int i = random.nextInt(j + 1);
            swap(a, i, j);
        }
        return a;
    }
    
    private void swap(int[] a, int i, int j) {
        int t = a[i];
        a[i] = a[j];
        a[j] = t;
    }
}　　

Python:

import random


class Solution(object):

    def __init__(self, nums):
        """
        :type nums: List[int]
        :type size: int
        """
        self.__nums = nums


    def reset(self):
        """
        Resets the array to its original configuration and return it.
        :rtype: List[int]
        """
        return self.__nums


    def shuffle(self):
        """
        Returns a random shuffling of the array.
        :rtype: List[int]
        """
        nums = list(self.__nums)
        for i in xrange(len(nums)):
            j = random.randint(i, len(nums)-1)
            nums[i], nums[j] = nums[j], nums[i]
        return nums


# Your Solution object will be instantiated and called as such:
# obj = Solution(nums)
# param_1 = obj.reset()
# param_2 = obj.shuffle()　　

C++:

class Solution {
public:
    Solution(vector<int> nums): v(nums) {}
    
    /** Resets the array to its original configuration and return it. */
    vector<int> reset() {
        return v;
    }
    
    /** Returns a random shuffling of the array. */
    vector<int> shuffle() {
        vector<int> res = v;
        for (int i = 0; i < res.size(); ++i) {
            int t = i + rand() % (res.size() - i);
            swap(res[i], res[t]);
        }
        return res;
    }
    
private:
    vector<int> v;
};