排序算法

内部排序：

1. 稳定排序（冒泡、插入、归并）：重复的元素一定按原始顺序排列

2. 非稳定排序（选择、快排）

外部排序：多路归并排序

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#define swap(a, b) { \
    __typeof(a) __temp = a; \
    a = b; b = __temp; \
}

#define TEST(arr, n, func) { \
    int *arr_test = (int *)malloc(sizeof(int) * n); \
    memcpy(arr_test, arr, sizeof(int) * n); \
    output(arr_test, n); \
    printf("%s = ", #func); \
    func(arr_test, n); \
    output(arr_test, n); \
    free(arr_test); \
    printf("\n"); \
}

void bubble_sort(int *arr, int n) {
    int flag = 1;
    for (int i = 0; i < n - 1 && flag; i++) {
        flag = 0; //如果flag始终没有被改变过，则证明序列已经是有序的
        for (int j = n - 1; j > i; j--) {
            if (arr[j] < arr[j - 1]) {
                swap(arr[j], arr[j - 1]);
                flag = 1;
            }
        }
    }
    return;
}

void insert_sort(int *arr, int n) {
    for (int i = 1; i < n; i++) {
        for (int j = i; j > 0 && arr[j] < arr[j - 1]; j--) {
            swap(arr[j], arr[j - 1]);
        }
    }
    return;
}

void merge_sort_recur(int *arr, int l, int r) {
    if (r - l <= 1) {
        if (r - l == 1 && arr[r] < arr[l]) swap(arr[r], arr[l]);
        return;
    }
    int mid = (l + r) >> 1;
    merge_sort_recur(arr, l, mid);
    merge_sort_recur(arr, mid + 1, r);
    int *temp = (int *)malloc(sizeof(int) * (r - l + 1));
    int p1 = l, p2 = mid + 1;
    for (int i = 0; p1 <= mid || p2 <= r; i++) {
        if (p2 > r || (p1 <= mid && arr[p1] < arr[p2])) {
            temp[i] = arr[p1++];
        } else {
            temp[i] = arr[p2++];
        }
    }
    memcpy(arr + l, temp, sizeof(int) * (r - l + 1));
    free(temp);
    return;
}

void merge_sort(int *arr, int n) {
    merge_sort_recur(arr, 0, n - 1);
    return;
}

void select_sort(int *arr, int n) {
    for (int i = 0; i < n; i++) {
        int index = i;
        for (int j = i + 1; j < n; j++) {
            if (arr[j] < arr[index]) index = j;
        }
        swap(arr[i], arr[index]);
    }
    return;
}

void quick_sort_recur(int *arr, int l, int r) {
    if (l >= r) return;
    int x = l, y = r, base = arr[l];
    while (x < y) {
        while (x < y && arr[y] >= base) y--;
        if (x < y) swap(arr[x], arr[y]);
        while (x < y && arr[x] <= base) x++;
        if (x < y) swap(arr[x], arr[y]);
    }
    arr[x] = base;
    quick_sort_recur(arr, l, x - 1);
    quick_sort_recur(arr, x + 1, r);
    return;
}

void quick_sort(int *arr, int n) {
    quick_sort_recur(arr, 0, n - 1);
    return;

}

void randint(int *arr, int n) {
    while (n--) arr[n] = rand() % 100; //判断的时候不减，判断完就已经减了，所以n的范围是[MAX_N - 1, 0]
    return;
}

void output(int *arr, int n) {
    printf("[");
    for (int i = 0; i < n; i++) {
        i && printf(" ");
        printf("%d", arr[i]);
    }
    printf("]\n");
}

int main() {
    srand(time(0));
    #define MAX_N 20
    int arr[MAX_N];
    randint(arr, MAX_N);
    TEST(arr, MAX_N, bubble_sort);
    TEST(arr, MAX_N, insert_sort);
    TEST(arr, MAX_N, merge_sort);
    TEST(arr, MAX_N, select_sort);
    TEST(arr, MAX_N, quick_sort);
    #undef MAX_N
    return 0;
}

快排退化与改进！！！