题目描述
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.
例子
例子 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]
Constraints
1 <= nums.length <= 200
-10^6 <= nums[i] <= 10^6
- All the elements of
nums
are unique.- At most
5 * 10^4
calls will be made toreset
andshuffle
.
解题思路
这里用到了一个水塘采样的算法来实现随机排列 n 个元素,证明过程这里不再赘述,有兴趣可以查阅相关资料。具体做法是:
- 从头开始遍历一遍数组
- 在 i 个元素时,在其后 n - i 个元素中随机选取一个元素
- 交换两元素
如此遍历一遍后则得到一个随机打乱的数组,代码如下:
#include <vector>
class Solution {
public:
Solution(std::vector<int>& nums) : nums_(nums) {}
/** Resets the array to its original configuration and return it. */
std::vector<int> reset() { return nums_; }
/** Returns a random shuffling of the array. */
std::vector<int> shuffle() {
std::vector<int> ans = nums_;
for (int i = 0; i < ans.size(); ++i) {
int n = i + rand() % (ans.size() - i);
std::swap(ans[i], ans[n]);
}
return ans;
}
private:
std::vector<int> nums_;
};
- 时间复杂度:
- 构造函数:
O(n)
reset(): O(1)
shuffule(): O(n)
- 构造函数:
- 空间复杂度:
O(n)
GitHub 代码同步地址: 384.ShuffleAnArray.cpp
其他题目: GitHub: Leetcode-C++-Solution 博客: Leetcode-Solutions