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解題 20. Shuffle an Array (隨機, 重設)

12 1 月, 2022 欣迪

出處： https://leetcode.com/explore/interview/card/top-interview-questions-easy/98/design/670/

Given an integer array nums, design an algorithm to randomly shuffle the array. All permutations of the array should be equally likely as a result of the shuffling.

Implement the Solution class:

• Solution(int[] nums) Initializes the object with the integer array nums.
• int[] reset() Resets the array to its original configuration and returns it.
• int[] shuffle() Returns a random shuffling of the array.

Example 1:

Input
["Solution", "shuffle", "reset", "shuffle"]
[[[1, 2, 3]], [], [], []]
Output
[null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]

Explanation
Solution solution = new Solution([1, 2, 3]);
solution.shuffle();    // Shuffle the array [1,2,3] and return its result.
                       // Any permutation of [1,2,3] must be equally likely to be returned.
                       // Example: return [3, 1, 2]
solution.reset();      // Resets the array back to its original configuration [1,2,3]. Return [1, 2, 3]
solution.shuffle();    // Returns the random shuffling of array [1,2,3]. Example: return [1, 3, 2]

Constraints:

• 1 <= nums.length <= 200
• -106 <= nums[i] <= 106
• All the elements of nums are unique.
• At most 5 * 104 calls in total will be made to reset and shuffle.

/**
 * @param {number[]} nums
 */
var Solution = function(nums) {
    this.nums = [...nums]
};

/**
 * @return {number[]}
 */
Solution.prototype.reset = function() {
    return this.nums
};

/**
 * @return {number[]}
 */
Solution.prototype.shuffle = function() {
    let nums = [...this.nums]
    for (let i = nums.length - 1; i > 0; i--) {
        const j = Math.floor(Math.random() * (i + 1))
        const temp = [nums[i], nums[j]]
        nums[i] = temp[1]
        nums[j] = temp[0]
    }
    return nums
};

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

這題其實有點像在考， this 在不同的作用域代表的意義。

常用技巧 : 取得 0 ~ n 之間的亂數整數

//  假設 n = 2 可能的結果是 0, 1, 2
const random = Math.floor(Math.random() * (n + 1))

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