[LeetCode] 384. Shuffle an Array 数组洗牌
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();
给一个没有重复数字的数组，实现重置和洗牌的功能。
解法：遍历数组每个位置，每次都随机生成一个坐标位置，然后交换当前位置和随机位置的数字，这样如果数组有n个数字，那么也随机交换了n组位置，从而达到了洗牌的目的。
Java:
import java.util.Random;
public 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() {
if(nums == null) return null;
int[] a = nums.clone();
for(int j = 1; j < a.length; j++) {
int i = random.nextInt(j + 1);
swap(a, i, j);
}
return a;
}
private void swap(int[] a, int i, int j) {
int t = a[i];
a[i] = a[j];
a[j] = t;
}
}
Python:
import random
class Solution(object):
def __init__(self, nums):
"""
:type nums: List[int]
:type size: int
"""
self.__nums = nums
def reset(self):
"""
Resets the array to its original configuration and return it.
:rtype: List[int]
"""
return self.__nums
def shuffle(self):
"""
Returns a random shuffling of the array.
:rtype: List[int]
"""
nums = list(self.__nums)
for i in xrange(len(nums)):
j = random.randint(i, len(nums)-1)
nums[i], nums[j] = nums[j], nums[i]
return nums
# Your Solution object will be instantiated and called as such:
# obj = Solution(nums)
# param_1 = obj.reset()
# param_2 = obj.shuffle()
C++:
class Solution {
public:
Solution(vector<int> nums): v(nums) {}
/** Resets the array to its original configuration and return it. */
vector<int> reset() {
return v;
}
/** Returns a random shuffling of the array. */
vector<int> shuffle() {
vector<int> res = v;
for (int i = 0; i < res.size(); ++i) {
int t = i + rand() % (res.size() - i);
swap(res[i], res[t]);
}
return res;
}
private:
vector<int> v;
};
