[leetcode]398. Random Pick Index

最新推荐文章于 2024-02-27 06:01:38 发布

xiaocong1990

最新推荐文章于 2024-02-27 06:01:38 发布

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本文链接：https://blog.youkuaiyun.com/xiaocong1990/article/details/54799984

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本文介绍了一种基于水塘抽样的算法实现，用于解决LeetCode上的一道题目：从包含可能重复元素的整数数组中随机返回给定目标值的一个索引。该算法能够保证每个符合条件的索引被选中的概率相同。

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题目链接：https://leetcode.com/problems/random-pick-index/

Given an array of integers with possible duplicates, randomly output the index of a given target number. You can assume that the given target number must exist in the array.

Note:
The array size can be very large. Solution that uses too much extra space will not pass the judge.

Example:

int[] nums = new int[] {1,2,3,3,3};
Solution solution = new Solution(nums);

// pick(3) should return either index 2, 3, or 4 randomly. Each index should have equal probability of returning.
solution.pick(3);

// pick(1) should return 0. Since in the array only nums[0] is equal to 1.
solution.pick(1);

解题思路：水塘抽样原理。见写过的一篇博客：http://blog.youkuaiyun.com/xiaocong1990/article/details/54286575

class Solution{
public:
    Solution(vector<int> nums)
    {
        this->nums=nums;
    }

    int pick(int target)
    {
        int index=0;
        int i=0;
        int count=0;
        while(i<nums.size())
        {
            if(nums[i]==target)
            {
                count+=1;
                int j=rand()%(count);
                if(j==0) index=i;

            }
            i++;
        }
        return index;
    }
private:
    vector<int> nums;
};