原文链接：tecdat.cn/?p=29614

Requirement

In this lab, each student is to write a program that allows the user to manipulate the entries in vector, or in a matrix. The program should keep track of one vector of variable length, and one matrix of exactly 4x4 size. The program should enter a loop, displaying a set of options (given below). Once the user selects an option, the program should display the vector (or matrix, as appropriate) before and after the operation chosen by the user. For example, if the user selects “reverse vector” and the current vector is [-3 0 2 5] then the program should display:

input  
-3 0 2 5  
reversed  
5 2 0 -1
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The program should run until the user selects an option to quit.
The program must use the following structure definitions.

struct vector {
  float *data;
  int    size;
};

struct matrix {
  struct vector rows[4];
};
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Analysis

Vectors和Matrices，矢量和矩阵，也称一维和二维数组。属于C语言很常见的数据结构。本题要实现的是矢量的反转，以及矩阵的转置。
反转和转置需要用到排序算法，这里我们采用Quicksort，也就是快速排序。

Tips

矢量反转所用的快速排序算法如下

int parition(struct vector *vec, int left, int right) {
  float piovt, temp;
  int i, j;
  piovt = *(vec[left]);
  i = left;
  j = right + 1;

  while (1) {
    do {
      ++i;
    } while (*(vec[i]) <= piovt && i <= right);
    do {
      --j;
    } while (*(vec[j]) > piovt);
    if (i >= j) {
      break;
    }
    temp = *(vec[i]);
    *(vec[i]) = *(vec[j]);
    *(vec[j]) = temp;
  }
  temp = *(vec[left]);
  *(vec[left]) = *(vec[right]);
  *(vec[right]) = temp;
  return j;
}
 
void quick_sort(struct vector *vec, int left, int right) {
  int i;
  if (left < right) {
    i = partition(vec, left, right);
    quick_sort(vec, left, right - 1);
    quick_sort(vec, i + 1, right);
  }
}
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