C++ 从一组数据中按概率选择一个

#include <stdio.h>
#include <stdint.h>
#include <ctime>
#include <vector>
#include <map>

template<typename T>
T *RandomSelect(const std::vector<T*> &itemPtrs);
uint32_t Random(uint32_t range);
uint32_t Random2(uint32_t range);

template<typename T>
T * RandomSelect(const std::vector<T*> &itemPtrs)
{
    if (itemPtrs.empty()){ return NULL; }
    uint32_t factor = ;
    std::vector<uint32_t> totalProbs;
    totalProbs.resize(itemPtrs.size());
    totalProbs[] = itemPtrs[]->Prob() * factor;
    ; i < itemPtrs.size(); ++i)
    {
        totalProbs[i] = totalProbs[i - ] + itemPtrs[i]->Prob() * factor;
    }
    uint32_t randInt = Random(totalProbs[totalProbs.size() - ]);
    ; i < totalProbs.size(); ++i)
    {
        if (randInt < totalProbs[i])
        {
            return itemPtrs[i];
        }
    }
    return NULL;
}

uint32_t Random(uint32_t range)
{
    ){ ; }
    return uint32_t((double)rand() / RAND_MAX * range) % range;
}

uint32_t Random2(uint32_t range)
{
    ){ ; }
    uint32_t rand1 = Random();
    uint32_t rand2 = Random();
    uint32_t rand3 = Random();
    uint32_t rand4 = Random();
    uint32_t num = (rand4 << ) | (rand3 << ) | (rand2 << ) | rand1;
    return uint32_t(double(num) / 0xFFFFFFFF * range) % range;
}

struct Item
{
    int32_t prob;
    Item(int32_t p) :prob(p){}
    int32_t Prob(){ return prob; }
};

int32_t main()
{
    std::map<Item*, int32_t> statistic;
    ;
    Item arrItem[] = { , , , , , , , , , ,  };
    std::vector<Item*> vecProbs;
    float sum = 0.0;
    ; j < ]); ++j)
    {
        sum += arrItem[j].Prob();
        vecProbs.push_back(&arrItem[j]);
    }
    ; i < loop; ++i)
    {
        Item *ret = RandomSelect(vecProbs);
        if (ret)
        {
            //printf("%d\n", ret->Prob());
            statistic[ret] += ;
        }
    }
    printf("statistic size = %u\n", statistic.size());
    double error = 0.0;
    for (const std::pair<Item*, int32_t> &p : statistic)
    {
        printf("%-8d %-8d %-12f %-12f\n", p.first->Prob(), p.second, (double)p.second / loop * 100.0, p.first->Prob() / sum * 100.0);
        error += fabs((double)p.second / loop * 100.0 - p.first->Prob() / sum * 100.0);
    }
    printf("error = %f\n", error);
    getchar();
    ;
}

事实证明,Random2要比Random的随机误差略小一点点,多随机几次还是有好处的.