Question
Formatted question description: https://leetcode.ca/all/384.html
384 Shuffle an Array
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();
Algorithm
Traverse each position of the array, randomly generate a coordinate position each time, and then exchange the number of the current traverse position and the randomly generated coordinate position.
If the array has n numbers, then we also randomly exchange n sets of positions, thus achieving the purpose of shuffling.
It should be noted here that i + rand()% (res.size()-i) cannot be written as rand()% res.size().
Code
Java
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class Shuffle_an_Array {
// 1. array deep copy
// 2. random.nextInt to dynamic list size
class Solution {
private int[] array;
private int[] original;
private Random rand = new Random();
private List<Integer> getArrayCopy() {
List<Integer> asList = new ArrayList<Integer>();
for (int i = 0; i < array.length; i++) {
asList.add(array[i]);
}
return asList;
}
public Solution(int[] nums) {
array = nums;
original = nums.clone();
}
public int[] reset() {
array = original;
original = original.clone();
return array;
}
public int[] shuffle() {
List<Integer> aux = getArrayCopy();
for (int i = 0; i < array.length; i++) {
int removeIdx = rand.nextInt(aux.size());
array[i] = aux.get(removeIdx);
aux.remove(removeIdx);
}
return array;
}
}
/**
* 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();
*/
}