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();
这个用到了洗牌算法：
1）将第1个元素与n个元素中的任意一个交换(包括自己)。这时结果中第1个元素已经确定。
2）将第2个元素与n-1个元素中作任意一个交换(包括自己)。
3）重复上面步骤，直到剩1个元素为止。
这样就可以返回随机排列的数组了。
public class Solution {
private int[] original;
private Random rng = new Random();
private int[] copy;
private int num;
public Solution(int[] nums) {
original = nums;
copy=original.clone();
num=original.length;
}
/** Resets the array to its original configuration and return it. */
public int[] reset() {
return original;
}
/** Returns a random shuffling of the array. */
public int[] shuffle() {
int n = num;
while(n>1) {
n--;
int k = rng.nextInt(n + 1);
int value = copy[k];
copy[k] = copy[n];
copy[n] = value;
}
return copy;
}
}
