算法導論第2章代碼

一、插入排序

算法：

void InsertionSort(int *a, int n)
{
    int i, j;
    for (i = 1; i < n; i++) {
        int key = a[i];
        j = i - 1;
        while (j >= 0 && a[j] > key) {
            a[j+1] = a[j];
            j--;
        }
        a[j+1] = key;
    }
}

測試：

int main(int argc, const char * argv[])
{
    int a[] = {3, 5, 1, 2, 5, 4};
    int n = sizeof(a) / sizeof(*a);
                                                           
                                                           
    InsertionSort(a, n);
                                                           
                                                           
    int i = 0;
    for (; i < n; i++) {
        printf("%d ", a[i]);
    }
                                                           
                                                           
    return 0;
}

輸出：1 2 3 4 5 5

二、歸併排序

算法：

void Merge(int *a, int low, int mid, int high)
{
    int i = low;
    int j = mid + 1;
    int *temp = malloc((high-low+1) * sizeof(int));
    int k = 0;
                     
    while (i <= mid && j <= high) {
                         
        if (a[i] <= a[j]) {
            temp[k++] = a[i++];
        }else{
            temp[k++] = a[j++];
        }
                         
    }
                     
    while (i <= mid) {
        temp[k++] = a[i++];
    }
                     
    while (j <= high) {
        temp[k++] = a[j++];
    }
                     
    for (i = low, k = 0; i <= high; i++, k++) {
        a[i] = temp[k];
    }
                     
    free(temp);
}
void MergeSort(int *a, int low, int high)
{
    if (low < high) {
        int mid = (low + high) / 2;
        MergeSort(a, low, mid);
        MergeSort(a, mid+1, high);
        Merge(a, low, mid, high);
    }
}

測試：

int main(int argc, const char * argv[])
{
    int a[] = {3, 5, 1, 2, 5, 4};
    int n = sizeof(a) / sizeof(*a);
    int low = 0;
    int high = n - 1;
           
    MergeSort(a, low, high);
           
    int i = 0;
    for (; i < n; i++) {
        printf("%d ", a[i]);
    }
           
    return 0;
}

輸出：1 2 3 4 5 5