LeetCode:384. Shuffle an Array

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    <p></p><p>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();

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              Fallible
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              Houzz
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              Hulu
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              Indeed
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              Intuit
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              LinkedIn
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              LiveRamp
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              Lyft
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              MAQ Software
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              Mathworks
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              Microsoft
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              NetEase
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              Netsuite
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              Palantir
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              Palantir Technologies
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              Pinterest
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              Pocket Gems
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              Poynt
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              Pure
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              Pure Storage
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              Rackspace
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              Riot
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              Riot Games
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              Snapchat
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              Square
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              Storage
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              Tencent
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              TinyCo
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              Twitter
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              Two Sigma
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              Works Applications
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              Yahoo
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              Yahoo!
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              Yelp
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              Zappos
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題意：洗牌或者復原。
分析：洗牌的過程就是等概率的返回全排列中的某一個排列，而全排列是通過相互交換位置得到的，因此，洗牌也可以通過相互交換位置得到。如何確定等概率，即兩兩交換的概率相同，因此有：
for(int i=0;i

class Solution {
    int[]base;
    public Solution(int[] nums) {
        base=nums;
    }

    /** Resets the array to its original configuration and return it. */
    public int[] reset() {
        return base;
    }

    /** Returns a random shuffling of the array. */
    public int[] shuffle() {
        int[]nums=base.clone();
        Random rand=new Random();
        for(int i=0;i<nums.length;i++){
            swap(nums,rand.nextInt(i+1),i);
        }
        return nums;
    }
    public void swap(int[]nums,int a,int b){
        int temp=nums[a];
        nums[a]=nums[b];
        nums[b]=temp;
    }
}

參考鏈接：http://bookshadow.com/weblog/2016/08/12/leetcode-shuffle-array/