实施算法（冒泡排序）来组织数组

Question

今天我正在练习编写一个程序，该程序基本上将用户的输入从最大值到最小值进行排序，并在排序后显示信息。为了做到这一点，我查阅了一些算法并遇到了冒泡排序方法。在阅读了一些文章之后，我了解了它的基本工作原理，因此我继续回顾了一些冒泡排序算法的示例编码，并将我从示例中学到的知识应用到了我的程序中。从我收到的输出来看，冒泡排序方法似乎在某种程度上有效。据我所知，我编写的冒泡排序算法/代码似乎只遍历数组一次，而不是遍历数组，直到所有整数都被排序到一个从最大值到最小值的列表中。有人可以帮我检查我的代码（尤其是冒泡排序部分）并指出正确的方向吗？

代码如下：

#include < iostream >

using namespace std;

int main() {
    int pancakes[10];
    int x;
    int valueSwitched;


    for (x = 0; x < 10; x++) {
        cout << "Please input the number of pancakes person " << (x + 1) << " has eaten.\n";
        cin >> pancakes[x];
    }

    for (int x = 0; x < 9; x++) {
        for (int y = 0; y < 9; y++) {
            if (pancakes[x] > pancakes[x + 1]) {
                int valueSwitched = pancakes[x];
                pancakes[x] = pancakes[x + 1];
                pancakes[x + 1] = valueSwitched;
            }
        }
    }

    cout << "\n-----ListSorted-----\n\n";

    for (int x = 0; x < 10; x++) {
        cout << "Person " << (x + 1) << " ate: " << pancakes[x] << endl;
    }

    return 0;
}

Answer 1

您的排序代码与

执行相同的操作

for (int x = 0; x < 9; x++) {
    if (pancakes[x] > pancakes[x + 1]) {
        int valueSwitched = pancakes[x];
        pancakes[x] = pancakes[x + 1];
        pancakes[x + 1] = valueSwitched;
    }
}

耗时 9 倍。

您将不得不交换x 和y 的循环。

for (int y = 0; y < 9; y++)
{
    for (int x = 0; x < 9; x++)
    {
        if (pancakes[x] > pancakes[x + 1])
        {
            int valueSwitched = pancakes[x];
            pancakes[x] = pancakes[x + 1];
            pancakes[x + 1] = valueSwitched;
        }
    }
}

或者为了更有效地做到这一点，试试这个：

for (int y = 9; y > 0; y--)
{
    for (int x = 0; x < y; x++)
    {
        if (pancakes[x] > pancakes[x + 1])
        {
            int valueSwitched = pancakes[x];
            pancakes[x] = pancakes[x + 1];
            pancakes[x + 1] = valueSwitched;
        }
    }
}

Answer 2

我在sorting 的数字中发现了一个问题。所以你需要先学习bubble sort。我对您的代码进行了一些更改。如下所示：

for (int x = 0; x < 9; x++) {
        for (int y = 0; y < 9-x; y++) {// changes
            if (pancakes[y] > pancakes[y + 1]) {//changes
                int valueSwitched = pancakes[y];
                pancakes[y] = pancakes[y + 1];
                pancakes[y + 1] = valueSwitched;
            }
        }
    }

现在输入9,8,7,6,5,4,3,2,1,0，它就可以工作了..

Answer 3

在循环的内部循环中，您正在比较和交换 pancakes[x] 和 pancakes[x + 1]，而不是比较和交换 pancakes[y] 和 pancakes[y + 1]。

for (int x = 0; x < 9; x++) {
    for (int y = 0; y < 9; y++) {
        if (pancakes[x] > pancakes[x + 1]) {
            int valueSwitched = pancakes[x];
            pancakes[x] = pancakes[x + 1];
            pancakes[x + 1] = valueSwitched;
        }
    }
}

我认为这只是一个错字。

不过我还是要指出，使用魔法并不是一个好主意 像 9 这样的数字。还有使用名称 i、j、k、l、m 和 n 作为索引的传统。

算法本身可以在数组已经排序后停止。

考虑到您可以使用标准函数std::swap 来交换数组的元素。

当数组已经排序后循环停止迭代时，我将展示这种方法

#include <iostream>

int main()
{
    const size_t N = 10;
    int pancakes[N];

    for ( size_t i = 0; i < N; i++ ) 
    {
        std::cout << "Please input the number of pancakes person " << i + 1 << " has eaten: ";
        std::cin >> pancakes[i];
    }

    size_t n = N;
    while ( !( n < 2 ) )
    {
        size_t last_sorted = 0;
        for ( size_t i = 1; i < n; i++) 
        {
            if ( pancakes[i-1] > pancakes[i] ) 
            {
                int valueSwitched = pancakes[i-1];
                pancakes[i-1] = pancakes[i];
                pancakes[i] = valueSwitched;
                last_sorted = i;
            }
        }

        n = last_sorted;
    }

    std::cout << "\n-----ListSorted-----\n\n";

    for ( size_t i = 0; i < N; i++ ) 
    {
        std::cout << "Person " << i + 1 << " ate: " << pancakes[i] << std::endl;
    }

    return 0;
}

如果以输入为例

10 1 9 2 8 3 7 4 6 5

你会得到

Please input the number of pancakes person 1 has eaten: 10
Please input the number of pancakes person 2 has eaten: 1
Please input the number of pancakes person 3 has eaten: 9
Please input the number of pancakes person 4 has eaten: 2
Please input the number of pancakes person 5 has eaten: 8
Please input the number of pancakes person 6 has eaten: 3
Please input the number of pancakes person 7 has eaten: 7
Please input the number of pancakes person 8 has eaten: 4
Please input the number of pancakes person 9 has eaten: 6
Please input the number of pancakes person 10 has eaten: 5

-----ListSorted-----

Person 1 ate: 1
Person 2 ate: 2
Person 3 ate: 3
Person 4 ate: 4
Person 5 ate: 5
Person 6 ate: 6
Person 7 ate: 7
Person 8 ate: 8
Person 9 ate: 9
Person 10 ate: 10

如果你想保持一个人和这个人吃的煎饼之间的关系，那么你应该声明一个对数组。

这是一个演示程序

#include <iostream>
#include <utility>

int main()
{
    const size_t N = 10;
    std::pair<size_t, int> pancakes[N];

    for ( size_t i = 0; i < N; i++ ) 
    {
        std::cout << "Please input the number of pancakes person " << i + 1 << " has eaten.\n";
        pancakes[i].first = i + 1;
        std::cin >> pancakes[i].second;
    }

    size_t n = N;
    while ( !( n < 2 ) )
    {
        size_t last_sorted = 0;
        for ( size_t i = 1; i < n; i++) 
        {
            if ( pancakes[i-1].second > pancakes[i].second ) 
            {
                auto valueSwitched = pancakes[i-1];
                pancakes[i-1] = pancakes[i];
                pancakes[i] = valueSwitched;
                last_sorted = i;
            }
        }

        n = last_sorted;
    }

    std::cout << "\n-----ListSorted-----\n\n";

    for ( size_t i = 0; i < N; i++ ) 
    {
        std::cout << "Person " << pancakes[i].first << " ate: " << pancakes[i].second << std::endl;
    }

    return 0;
}

对于与上面相同的输入，其排序后的输出将如下所示

-----ListSorted-----

Person 2 ate: 1
Person 4 ate: 2
Person 6 ate: 3
Person 8 ate: 4
Person 10 ate: 5
Person 9 ate: 6
Person 7 ate: 7
Person 5 ate: 8
Person 3 ate: 9
Person 1 ate: 10