Description
Shuffle a set of numbers without duplicates.
Example:
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
Random
经典的shuffle算法，随机&交换。注意random.nextInt(n)返回值是[0, n)范围内的随机值。
class Solution {
private int[] nums;
private Random random;
public Solution(int[] nums) {
this.nums = nums;
random = new Random();
}
/** Resets the array to its original configuration and return it. */
public int[] reset() {
return nums;
}
/** Returns a random shuffling of the array. */
public int[] shuffle() {
int[] shuffle = nums.clone();
for (int i = shuffle.length; i > 0; --i) {
int j = (int) random.nextInt(i); // returns x between [0, i)
swap(shuffle, j, i - 1);
}
return shuffle;
}
private void swap(int[] nums, int i, int j) {
int tmp = nums[i];
nums[i] = nums[j];
nums[j] = tmp;
}
}
/**
* 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();
*/
