Question

这是我实现选择排序的代码，但输出的顺序不正确。有人可以告诉我问题在哪里吗？

所以这是我实现选择排序的代码：

#include <iostream>
using namespace std;

class sort {
public:
    void ssort(string[], int[]);
    void print(string[], int);

};

// sorting function
// is the problem here?
void sort::ssort(string arr[], int numarray[]) {
    int min;

    for (int i = 0; i < 8; ++i)
    {
        min = i;
        //Loop through the array to find it
        for (int j = i + 1; j < 9; ++j)
        {
            if (numarray[j] < numarray[min])
            {
                //Found new minimum position, if present
                min = j;
            }
        }
        //Swap the values
        swap(arr[i], arr[min]);
    }
}

void sort::print(string arr[], int num) {
    for (int i = 0; i < num; ++i)
    {
        cout << arr[i] << endl;
    }
    cout << endl;
}

//main function
main() {
    sort s;
    int num = 8;
    string arr[8];
    string array[8];
    int numarray[8];


    cout << "Input 8 strings to sort: " << endl;
    for (int i = 0; i < 8; i++) {
        getline(cin, arr[i]);
    }
    cout << endl;

    for (int i = 0; i < 8; i++) {
        array[i] = arr[i].substr(0, 1);

        if (array[i] == "a")
            numarray[i] = 1;
        if (array[i] == "b")
            numarray[i] = 2;
        if (array[i] == "c")
            numarray[i] = 3;
        if (array[i] == "d")
            numarray[i] = 4;
        if (array[i] == "e")
            numarray[i] = 5;
        if (array[i] == "f")
            numarray[i] = 6;
        if (array[i] == "g")
            numarray[i] = 7;
        if (array[i] == "h")
            numarray[i] = 8;
        if (array[i] == "i")
            numarray[i] = 9;
        if (array[i] == "j")
            numarray[i] = 10;
        if (array[i] == "k")
            numarray[i] = 11;
        if (array[i] == "l")
            numarray[i] = 12;
        if (array[i] == "m")
            numarray[i] = 13;
        if (array[i] == "n")
            numarray[i] = 14;
        if (array[i] == "o")
            numarray[i] = 15;
        if (array[i] == "p")
            numarray[i] = 16;
        if (array[i] == "q")
            numarray[i] = 17;
        if (array[i] == "r")
            numarray[i] = 18;
        if (array[i] == "s")
            numarray[i] = 19;
        if (array[i] == "t")
            numarray[i] = 20;
        if (array[i] == "u")
            numarray[i] = 21;
        if (array[i] == "v")
            numarray[i] = 22;
        if (array[i] == "w")
            numarray[i] = 23;
        if (array[i] == "x")
            numarray[i] = 24;
        if (array[i] == "y")
            numarray[i] = 25;
        if (array[i] == "z")
            numarray[i] = 26;

    }

    cout << "The Initial Input: " << endl;
    s.print(arr, num);

    s.ssort(arr, numarray);

    cout << endl << "The input after sorting: " << endl;
    s.print(arr, num);
}

我该怎么办？

Answer 1

我通过快速阅读您的代码确定了三个问题：

首先内循环条件错误

void sort::ssort(string arr[], int numarray[]) {
  int min;

  for (int i = 0; i < 8; ++i) {
    min = i;
    //Loop through the array to find it
    for (int j = i + 1; j < 9; ++j) // Out-of-bound access on j == 8

第二：您的ssort函数只会根据第一个字符对字符串进行排序。它并没有真正对字符串进行排序。

第三个（这是一个很大的算法错误）：交换numarray元素后，您没有交换arr向量元素。这意味着第一个之后的所有掉期（指数位于正确的位置）可能错误。

void sort::ssort(string arr[], int numarray[]) {
  int min;

  for (int i = 0; i < 8; ++i)
  {
    min = i;
    //Loop through the array to find it
    for (int j = i + 1; j < 8; ++j)
    {
      if (numarray[j] < numarray[min])
      {
          //Found new minimum position, if present
        min = j;
      }
    }
    //Swap the values
    swap(arr[i], arr[min]);
    // Also swap the comparison values
    swap(numarray[i], numarray[min]); // <-- this is missing!
  }
}

改善提示：

拿一本好的算法书并研究它
抓住一个好的调试器并使用它

Answer 2

您应该更新numarray以及arr，并且无法访问越界。

void sort::ssort(string arr[], int numarray[]) {
    int min;

    for (int i = 0; i < 8; ++i)
    {
        min = i;
        //Loop through the array to find it
        for (int j = i + 1; j < 8; ++j) // fix : 9 -> 8
        {
            if (numarray[j] < numarray[min])
            {
                //Found new minimum position, if present
                min = j;
            }
        }
        //Swap the values
        swap(arr[i], arr[min]);
        swap(numarray[i], numarray[min]); // add this line
    }
}

如何修复我的代码以进行选择排序？

2 个答案: