LeetCode-探索-初级算法-设计问题-1. Shuffle an Array(个人做题记录，不是习题讲解)

LeetCode-探索-初级算法-设计问题-1. Shuffle an Array(个人做题记录，不是习题讲解)

LeetCode探索-初级算法：https://leetcode-cn.com/explore/interview/card/top-interview-questions-easy/

1. Shuffle an Array

• 语言：java

• 思路：看了网上说打乱的方法就是从尾部到头部遍历的时候生成随机数，然后进行位置调换。还原就没什么好说的了。

  https://blog.csdn.net/m0_38082783/article/details/79579116

• 代码(218ms,84.32%，还行吧)：

  class Solution {
  
      public int[] raw;
      public int[] backpack;
      public int len;
      
      public Solution(int[] nums) {
          raw = nums;
          len = nums.length;
          backpack = new int[len];
          System.arraycopy(nums,0,backpack,0,len);
      }
      
      /** Resets the array to its original configuration and return it. */
      public int[] reset() {
          return raw;
      }
      
      /** Returns a random shuffling of the array. */
      public int[] shuffle() {
          for(int i = len - 1; i >= 0; --i){
              int j = (int)(Math.random() * len);
              int tmp = backpack[i];
              backpack[i] = backpack[j];
              backpack[j] = tmp;
          }
          return backpack;
      }
  }
  
  /**
   * 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();
   */
  

• 参考代码(120ms)：整体思路时一样的，都是从尾到头，生成随机数来表示替换的下标，然后进行"随机“替换

  class Solution {
      private int[] original;
      private int[] arr;
      private Random r;
  
      public Solution(int[] nums) {
          original = nums;
          arr = Arrays.copyOf(nums, nums.length);
          r = new Random();
      }
      
      /** Resets the array to its original configuration and return it. */
      public int[] reset() {
          System.arraycopy(original, 0, arr, 0, original.length);
          return arr;
      }
      
      /** Returns a random shuffling of the array. */
      public int[] shuffle() {
          for(int n = arr.length; n > 1; n--) {
              swap(arr, n - 1, r.nextInt(n));
          }
          return arr;
      }
      
      private void swap(int[] nums, int i, int j) {
          int temp = nums[i];
          nums[i] = nums[j];
          nums[j] = temp;
      }
  }
  
  /**
   * 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();
   */