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();
Solution：Reservoir Sampling
思路：
Time Complexity: O(N) Space Complexity: O(N)
Solution Code：
class Solution {
public Solution(int[] nums) {
// copy a original
copy = new int[nums.length];
for(int i = 0; i < nums.length; i++) {
copy[i] = nums[i];
}
// cur
cur = new int[nums.length];
for(int i = 0; i < nums.length; i++) {
cur[i] = nums[i];
}
rand = new Random();
}
/** Resets the array to its original configuration and return it. */
public int[] reset() {
return copy;
}
/** Returns a random shuffling of the array. */
public int[] shuffle() {
int slow = 0;
for(int fast = 0; fast < cur.length; fast++) {
slow = rand.nextInt(fast + 1);
swap(cur, fast, slow);
}
return cur;
}
private void swap(int[] nums, int a, int b) {
int tmp = nums[a];
nums[a] = nums[b];
nums[b] = tmp;
}
private int[] copy;
private int[] cur;
private Random rand;
}
