ID | Title | Difficulty | |
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384. Shuffle an Array
Medium
LeetCode
Array, Math, Randomized
Problem
Given an integer array nums, design an algorithm to randomly shuffle the array.
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]
Code
Fisher-Yates Shuffle
class Solution {
private int[] nums;
private Random rand;
public Solution(int[] nums) {
this.nums = nums;
rand = new Random();
}
public int[] reset() {
return nums;
}
public int[] shuffle() {
int[] clone = nums.clone();
for(int end = nums.length - 1; end >= 0; end--){
int randNum = rand.nextInt(end + 1);
swap(clone, randNum, end);
}
return clone;
}
private void swap(int[] nums, int i, int j){
int temp = nums[i];
nums[i] = nums[j];
nums[j] = temp;
}
}
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