Given an integer array nums, design an algorithm to randomly shuffle the array. All permutations of
the array should be equally likely as a result of the shuffling.
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.
Example 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 <= 200-106 <= nums[i] <= 106- All the elements of
numsare unique. - At most
5 * 104calls in total will be made toresetandshuffle.
Solution:
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/**
* Optimized solution is : Fisher-Yates Algorithm
* This involves following steps
* 1. Start with first index say start.
* 2. Pick a random index from range [start, arr.length)
* 3. Swap start index element with element at random index.
* 4. Increment start and continue above steps till end is reached.
* Time Complexity: O(N)
* Space Complexity: O(N).
*/
class Solution {
int[] a;
public Solution(int[] nums) {
a = nums;
}
/**
* Resets the array to its original configuration and return it.
*/
public int[] reset() {
return a;
}
/**
* Returns a random shuffling of the array.
*/
public int[] shuffle() {
int[] res = a.clone();
for (int i = 0; i < res.length; i++) {
int rand = i + (int) (Math.random() * (res.length - i));
int temp = res[i];
res[i] = res[rand];
res[rand] = temp;
}
return res;
}
}
/**
* 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();
*/