Randomized quickSort

最新推荐文章于 2023-04-16 00:04:30 发布

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本文介绍了一种使用C++实现的快速排序算法，并详细展示了如何通过随机化选取枢轴来优化排序过程，提高算法效率。代码示例清晰地说明了随机化快速排序的具体实现方法。

C/C++中产生随机数(rand,srand用法)
http://blog.youkuaiyun.com/PYPARA/article/details/54773968
Quick sort
http://blog.youkuaiyun.com/pypara/article/details/54773861

C++：

int partition(int *a, int lhs, int rhs);
int RandomizedPartition(int *a, int lhs, int rhs) {
    int rad = (rand() % (rhs - lhs + 1)) + lhs;
    int pivot = a[rad];
    int temp = a[lhs];
    a[lhs] = pivot;
    a[rad] = temp;
    return partition(a, lhs, rhs);

}

void RandomizedQuickSort(int *a, int lhs, int rhs) {
    if (lhs >= rhs) {
        return;
    }
    int q = RandomizedPartition(a, lhs, rhs);
    RandomizedQuickSort(a, lhs, q);
    RandomizedQuickSort(a, q + 1, rhs);
}


int partition(int *a, int lhs, int rhs) {
    int i = lhs;
    int j = lhs + 1;
    int pivot = a[lhs];
    while (j <= rhs) {
        if (a[j] >= pivot) {
            ++j;
        }
        else {
            ++i;
            int temp = a[i];
            a[i] = a[j];
            a[j] = temp;
            ++j;
        }
    }
    int temp2 = a[i];
    a[i] = pivot;
    a[lhs] = temp2;
    return i;
}



void QuickSort(int *a, int lhs, int rhs) {
    if (lhs >= rhs) {
        return;
    }
    int q = partition(a, lhs, rhs);
    QuickSort(a, lhs, q);
    QuickSort(a, q + 1, rhs);
}

Text：

#include<iostream>
int partition(int *a, int lhs, int rhs);
int RandomizedPartition(int *a, int lhs, int rhs) {
    int rad = (rand() % (rhs - lhs + 1)) + lhs;
    int pivot = a[rad];
    int temp = a[lhs];
    a[lhs] = pivot;
    a[rad] = temp;
    return partition(a, lhs, rhs);

}

void RandomizedQuickSort(int *a, int lhs, int rhs) {
    if (lhs >= rhs) {
        return;
    }
    int q = RandomizedPartition(a, lhs, rhs);
    RandomizedQuickSort(a, lhs, q);
    RandomizedQuickSort(a, q + 1, rhs);
}


int partition(int *a, int lhs, int rhs) {
    int i = lhs;
    int j = lhs + 1;
    int pivot = a[lhs];
    while (j <= rhs) {
        if (a[j] >= pivot) {
            ++j;
        }
        else {
            ++i;
            int temp = a[i];
            a[i] = a[j];
            a[j] = temp;
            ++j;
        }
    }
    int temp2 = a[i];
    a[i] = pivot;
    a[lhs] = temp2;
    return i;
}



void QuickSort(int *a, int lhs, int rhs) {
    if (lhs >= rhs) {
        return;
    }
    int q = partition(a, lhs, rhs);
    QuickSort(a, lhs, q);
    QuickSort(a, q + 1, rhs);
}

int main() {

    int a[22] = { 9,8,7,6,5,4,3,2,1,0,5,65,435,224,234,84,642,32,13,87,215,21 };
    RandomizedQuickSort(a, 0, 21);
    for (auto c : a) {
        std::cout << c << " ";
    }
    std::cout << std::endl;
    return 0;
}