LeetCode Top Interview Questions 384. Shuffle an Array (Java版; Meidum)

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LeetCode Top Interview Questions 384. Shuffle an Array (Java版; Meidum)

题目描述

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();

第一次做; 主要是弄明白下面题解中洗牌算法的本质: 如果有n张牌, 那么洗牌的结果应该是等可能的n!种 采用交换的方式进行洗牌的算法貌似叫做Fisher-Yates算法, 有四种写法, 看下面的题解; 注意生成随机整数的方法, 可以使用rand.nextInt(max - min) + min;这种写法获取[a,b)区间上的随机整数

class Solution {
    private Random random;
    int[] ori;
    int[] nums;
    public Solution(int[] nums) {
        ori = Arrays.copyOf(nums, nums.length);
        random = new Random();
        this.nums = nums;
    }
    
    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        nums = Arrays.copyOf(ori, ori.length);
        return nums;
    }
    
    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        //洗牌算法, 牢记:n张牌的洗牌结果应该有n!种, 每种结果都是等可能
        int n = nums.length;
        for(int i=n-1; i>=0; i--){
            int index = random.nextInt(i+1);
            swap(nums, i, index);
        }
        return nums;
    }
    
    private void swap(int[] arr, int i, int j){
        int tmp = arr[i];
        arr[i] = arr[j];
        arr[j] = tmp;
    }
}

/**
 * Your Solution object will be instantiated and called as such:
 * Solution obj = new Solution(nums);
 * int[] param_1 = obj.reset();
 * int[] param_2 = obj.shuffle();
 */

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