# ===== CodeLab: c-sorting =====
# 以下代码片段按文章出现顺序拼接, 共 7 段

# ----- 片段 1 (c) -----
#include <stdio.h>

void swap(int *a, int *b) {
    int t = *a;
    *a = *b;
    *b = t;
}

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

# ----- 片段 2 (c) -----
void bubble_sort(int arr[], int n) {
    for (int i = 0; i < n - 1; i++) {
        int swapped = 0;                 /* 本轮有没有发生交换 */
        for (int j = 0; j < n - 1 - i; j++) {
            if (arr[j] > arr[j + 1]) {
                swap(&arr[j], &arr[j + 1]);
                swapped = 1;
            }
        }
        if (!swapped) {
            break;                       /* 一轮没交换 = 已经有序 */
        }
    }
}

# ----- 片段 3 (c) -----
void selection_sort(int arr[], int n) {
    for (int i = 0; i < n - 1; i++) {
        int min_idx = i;
        for (int j = i + 1; j < n; j++) {
            if (arr[j] < arr[min_idx]) {
                min_idx = j;
            }
        }
        if (min_idx != i) {
            swap(&arr[i], &arr[min_idx]);
        }
    }
}

# ----- 片段 4 (c) -----
void insertion_sort(int arr[], int n) {
    for (int i = 1; i < n; i++) {
        int key = arr[i];
        int j = i - 1;
        while (j >= 0 && arr[j] > key) {
            arr[j + 1] = arr[j];   /* 右移腾位 */
            j--;
        }
        arr[j + 1] = key;
    }
}

# ----- 片段 5 (c) -----
int partition(int arr[], int low, int high) {
    int pivot = arr[high];
    int i = low - 1;             /* i 左边都是 <= pivot 的 */
    for (int j = low; j < high; j++) {
        if (arr[j] < pivot) {
            i++;
            swap(&arr[i], &arr[j]);
        }
    }
    swap(&arr[i + 1], &arr[high]);  /* 基准归位 */
    return i + 1;
}

void quick_sort(int arr[], int low, int high) {
    if (low < high) {
        int p = partition(arr, low, high);
        quick_sort(arr, low, p - 1);
        quick_sort(arr, p + 1, high);
    }
}

# ----- 片段 6 (c) -----
#include <stdlib.h>

void merge(int arr[], int left, int mid, int right) {
    int n1 = mid - left + 1;
    int n2 = right - mid;
    int *L = (int *)malloc(n1 * sizeof(int));
    int *R = (int *)malloc(n2 * sizeof(int));
    for (int i = 0; i < n1; i++) L[i] = arr[left + i];
    for (int j = 0; j < n2; j++) R[j] = arr[mid + 1 + j];

    int i = 0, j = 0, k = left;
    while (i < n1 && j < n2) {
        if (L[i] <= R[j]) arr[k++] = L[i++];
        else arr[k++] = R[j++];
    }
    while (i < n1) arr[k++] = L[i++];
    while (j < n2) arr[k++] = R[j++];
    free(L);
    free(R);
}

void merge_sort(int arr[], int left, int right) {
    if (left >= right) return;
    int mid = left + (right - left) / 2;
    merge_sort(arr, left, mid);
    merge_sort(arr, mid + 1, right);
    merge(arr, left, mid, right);
}

# ----- 片段 7 (c) -----
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

/* 前面五种排序函数都放到这里 */

int main(void) {
    const int N = 20000;
    int *base = (int *)malloc(N * sizeof(int));
    int *tmp = (int *)malloc(N * sizeof(int));
    clock_t start, end;

    srand((unsigned)time(NULL));
    for (int i = 0; i < N; i++) {
        base[i] = rand() % 1000000;
    }

    memcpy(tmp, base, N * sizeof(int));
    start = clock();
    bubble_sort(tmp, N);
    end = clock();
    printf("bubble:    %.3f s\n", (double)(end - start) / CLOCKS_PER_SEC);

    memcpy(tmp, base, N * sizeof(int));
    start = clock();
    selection_sort(tmp, N);
    end = clock();
    printf("selection: %.3f s\n", (double)(end - start) / CLOCKS_PER_SEC);

    memcpy(tmp, base, N * sizeof(int));
    start = clock();
    insertion_sort(tmp, N);
    end = clock();
    printf("insertion: %.3f s\n", (double)(end - start) / CLOCKS_PER_SEC);

    memcpy(tmp, base, N * sizeof(int));
    start = clock();
    quick_sort(tmp, 0, N - 1);
    end = clock();
    printf("quick:     %.3f s\n", (double)(end - start) / CLOCKS_PER_SEC);

    memcpy(tmp, base, N * sizeof(int));
    start = clock();
    merge_sort(tmp, 0, N - 1);
    end = clock();
    printf("merge:     %.3f s\n", (double)(end - start) / CLOCKS_PER_SEC);

    free(base);
    free(tmp);
    return 0;
}