随机算法

Posted 2021-01-08 liuweimingcprogram

Fisher–Yates shuffle 洗牌算法



海量数据随机抽样问题（蓄水池问题）

题目

class Solution {
private:
    vector<int> vc;
public:
    Solution(vector<int> nums) {
        vc = nums;
    }
    
    int pick(int target) {
        vector<int> tmp;
        int size = 0;
        for (int i = 0; i < vc.size(); ++i) {
            if (target == vc[i]) {
                if (tmp.size() != 0) {
                    int lim = 66666666 - 66666666 % i;
                    int id = rand();
                    while (id > lim) id = rand();
                    id %= ++size;
                    if (id == 0) tmp[id] = i;
                } else {
                    ++size;
                    tmp.push_back(i);
                }
            }
        }
        return tmp[0];
    }
};

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