C 排序算法冒泡排序

选择排序（Selection sort）是一种简单直观的排序算法。它的工作原理如下。首先在未排序序列中找到最小（大）元素，存放到排序序列的起始位置，然后，再从剩余未排序元素中继续寻找最小（大）元素，然后放到已排序序列的末尾。以此类推，直到所有元素均排序完毕。

#include <stdio.h>

void selection_sort(int a[], int len) {
    int i,
    j,
    temp;
    for (i = 0; i < len - 1; i++) {
        int min = i;
        for (j = i + 1; j < len; j++) {
            if (a[j] < a[min]) {
                min = j;
            }
        }
        if(min != i) {
            temp = a[min];
            a[min] = a[i];
            a[i] = temp;
        }
    }
}

int main() {
   int arr[] = { 22, 34, 3, 32, 82, 55, 89, 50, 37, 5, 64, 35, 9, 70 }; 
   int len = (int) sizeof(arr) / sizeof(*arr);
   
   selection_sort(arr, len);  
   
   int i; 
   for (i = 0; i < len; i++) 
      printf("%d \n", arr[i]);
      
   return 0;
}

插入排序（英语：Insertion Sort）是一种简单直观的排序算法。它的工作原理是通过构建有序序列，对于未排序数据，在已排序序列中从后向前扫描，找到相应位置并插入。插入排序在实现上，通常采用in-place排序（即只需用到 {\displaystyle O(1)} {\displaystyle O(1)}的额外空间的排序），因而在从后向前扫描过程中，需要反复把已排序元素逐步向后

挪位，为最新元素提供插入空间。

#include <stdio.h>
void insertion_sort(int arr[], int len){
    int i,j,temp;

    for (i=1;i<len;i++){
    temp = arr[i];

        for (j=i;j>0 && arr[j-1]>temp;j--)  
            arr[j] = arr[j-1];   
            arr[j] = temp;    
    }
}
int main() {
   int arr[] = { 22, 34, 3, 32, 82, 55, 89, 50, 37, 5, 64, 35, 9, 70 }; 
   int len = (int) sizeof(arr) / sizeof(*arr);
   
   insertion_sort(arr, len);  
   
   int i; 
   for (i = 0; i < len; i++) 
      printf("%d \n", arr[i]);
      
   return 0;
}

希尔排序，也称递减增量排序算法，是插入排序的一种更高效的改进版本。希尔排序是非稳定排序算法。

希尔排序是基于插入排序的以下两点性质而提出改进方法的：

• 插入排序在对几乎已经排好序的数据操作时，效率高，即可以达到线性排序的效率
• 但插入排序一般来说是低效的，因为插入排序每次只能将数据移动一位

#include <stdio.h>
void shell_sort(int arr[], int len) {
int gap, i, j;
int temp;

for (gap = len >> 1; gap > 0; gap = gap >> 1)
for (i = gap; i < len; i++) {
temp = arr[i];


     for (j = i - gap; j >= 0 && arr[j] > temp; j -= gap)    
        arr[j + gap] = arr[j];  
                          
        arr[j + gap] = temp;       
     }    
}
int main() {
   int arr[] = { 22, 34, 3, 32, 82, 55, 89, 50, 37, 5, 64, 35, 9, 70 }; 
   int len = (int) sizeof(arr) / sizeof(*arr);
   
   shell_sort(arr, len);  
   
   int i; 
   for (i = 0; i < len; i++) 
      printf("%d \n", arr[i]);
      
   return 0;
}

把数据分为两段，从两段中逐个选最小的元素移入新数据段的末尾。

可从上到下或从下到上进行。

#include <stdio.h>
int min(int x, int y) {
    return x < y ? x : y;
}

void merge_sort(int arr[], int len) {
    int* a = arr;
    int* b = (int*) malloc(len * sizeof(int));
    int seg, start;
    for (seg = 1; seg < len; seg += seg) {
        for (start = 0; start < len; start += seg + seg) {
            int low = start, mid = min(start + seg, len), high = min(start + seg + seg, len);
            int k = low;
            int start1 = low, end1 = mid;
            int start2 = mid, end2 = high;
            while (start1 < end1 && start2 < end2)
                b[k++] = a[start1] < a[start2] ? a[start1++] : a[start2++];
            while (start1 < end1)
                b[k++] = a[start1++];
            while (start2 < end2)
                b[k++] = a[start2++];
        }
        int* temp = a;
        a = b;
        b = temp;
    }
    if (a != arr) {
        int i;
        for (i = 0; i < len; i++)
            b[i] = a[i];
        b = a;
    }
    free(b);
}

int main() {
   int arr[] = { 22, 34, 3, 32, 82, 55, 89, 50, 37, 5, 64, 35, 9, 70 }; 
   int len = (int) sizeof(arr) / sizeof(*arr);
   
   merge_sort(arr, len);  
   
   int i; 
   for (i = 0; i < len; i++) 
      printf("%d \n", arr[i]);
      
   return 0;
}

#include <stdio.h>
void merge_sort_recursive(int arr[], int reg[], int start, int end) {
    if (start >= end)
        return;
    int len = end - start;
    int mid = (len >> 1) + start;
    int start1 = start, end1 = mid;
    int start2 = mid + 1, end2 = end;

    merge_sort_recursive(arr, reg, start1, end1);
    merge_sort_recursive(arr, reg, start2, end2);

    int k = start;
    while (start1 <= end1 && start2 <= end2)
        reg[k++] = arr[start1] < arr[start2] ? arr[start1++] : arr[start2++];

    while (start1 <= end1)
        reg[k++] = arr[start1++];

    while (start2 <= end2)
        reg[k++] = arr[start2++];

    for (k = start; k <= end; k++)
        arr[k] = reg[k];
}

void merge_sort(int arr[], const int len) {
    int reg[len];
    merge_sort_recursive(arr, reg, 0, len - 1);
}


int main() {
   int arr[] = { 22, 34, 3, 32, 82, 55, 89, 50, 37, 5, 64, 35, 9, 70 }; 
   int len = (int) sizeof(arr) / sizeof(*arr);
   
   merge_sort(arr, len);  
   
   int i; 
   for (i = 0; i < len; i++) 
      printf("%d \n", arr[i]);
      
   return 0;
}

快速排序

在区间中随机挑选一个元素作基准，将小于基准的元素放在基准之前，大于基准的元素放在基准之后，再分别对小数区与大数区进行排序。

#include <stdio.h>
typedef struct _Range {
    int start, end;
} Range;

Range new_Range(int s, int e) {
    Range r;
    r.start = s;
    r.end = e;
    return r;
}

void swap(int *x, int *y) {
    int t = *x;
    *x = *y;
    *y = t;
}

void quick_sort(int arr[], const int len) {
    if (len <= 0)
        return;

    // r[] simulates a stack
    // p is the size of the stack
    // r[p++] is equivalent to push
    // r[--p] is equivalent to pop and get the element
    Range r[len];
    int p = 0;
    r[p++] = new_Range(0, len - 1);

    while (p) {
        Range range = r[--p];
        if (range.start >= range.end)
            continue;

        int mid = arr[(range.start + range.end) / 2]; // Select the middle element as the pivot

        int left = range.start, right = range.end;
        do {
            while (arr[left] < mid)
                ++left; // Check if elements on the left side of the pivot satisfy the condition
            while (arr[right] > mid)
                --right; // Check if elements on the right side of the pivot satisfy the condition

            if (left <= right) {
                swap(&arr[left], &arr[right]);
                left++;
                right--; // Move pointers to continue
            }
        } while (left <= right);

        if (range.start < right)
            r[p++] = new_Range(range.start, right);
        if (range.end > left)
            r[p++] = new_Range(left, range.end);
    }
}


int main() {
   int arr[] = { 22, 34, 3, 32, 82, 55, 89, 50, 37, 5, 64, 35, 9, 70 }; 
   int len = (int) sizeof(arr) / sizeof(*arr);
   
   quick_sort(arr, len);  
   
   int i; 
   for (i = 0; i < len; i++) 
      printf("%d \n", arr[i]);
      
   return 0;
}

#include <stdio.h>
void swap(int *x, int *y) {
    int t = *x;
    *x = *y;
    *y = t;
}

void quick_sort_recursive(int arr[], int start, int end) {
    if (start >= end)
        return;

    int mid = arr[end];
    int left = start, right = end - 1;

    while (left < right) {
        while (arr[left] < mid && left < right)
            left++;
        while (arr[right] >= mid && left < right)
            right--;

        swap(&arr[left], &arr[right]);
    }

    if (arr[left] >= arr[end])
        swap(&arr[left], &arr[end]);
    else
        left++;

    if (left)
        quick_sort_recursive(arr, start, left - 1);
    quick_sort_recursive(arr, left + 1, end);
}

void quick_sort(int arr[], int len) {
    quick_sort_recursive(arr, 0, len - 1);
}

int main() {
   int arr[] = { 22, 34, 3, 32, 82, 55, 89, 50, 37, 5, 64, 35, 9, 70 }; 
   int len = (int) sizeof(arr) / sizeof(*arr);
   
   quick_sort(arr, len);  
   
   int i; 
   for (i = 0; i < len; i++) 
      printf("%d \n", arr[i]);
      
   return 0;
}