算法导论 第二章 简单排序算法－－插入排序，冒泡排序，选择排序

插入排序

/*
 * Insertion_sort time complexity:
 * Best-case: if the original sequence is sorted in a wanted-order: O(n)
 * Worst-case: if the original array is sorted in a reverse order: O(n^2)
 */
void insertion_sort(int a[], int n)
{
    int i, j, key;
    for (j = 1; j < n; ++j) {
        key = a[j];
        i = j - 1;
        while (i >= 0 && a[i] > key) {
            a[i+1] = a[i];
            --i;
        }
        a[i+1] = key;
    }

}

冒泡排序

/*
 * 算法复杂度 O(n^2)
 */
void BubbleSort(int a[], int n)
{
    int i, j, temp;
    //int flag = 0;
 
    for (i = 0; i < n; ++i) {
        //flag = 0;
        for (j = n-1; j > i; --j) {
            if (a[j] < a[j-1]) {
                //flag = 1;
                temp = a[j];
                a[j] = a[j-1];
                a[j-1] = temp;
            }
        }
       // if (flag == 0)
       //     break;
    }
}

选择排序：

/*
 * Selection_sort(A)
 * First find the smallest element of A and exchang it with A[1],
 * then find the second smallest element of A and exchang it with A[2]
 * continue this manner for the first n-1 elements of A.
 * Runnig time:
 * O(n^2) both in the Best and Worst-case.
 */
int find_min(int a[], int start, int end)
{
    int i;
    int res = start;
    for (i = start+1; i < end; ++i)
        if (a[res] > a[i])
            res = i;
    return res;
}
 
void selection_sort(int a[], int n)
{
    int j, k;
    int temp;
    for (j = 0; j < n-1; ++j) {
        k = j;
        k = find_min(a, j, n);
        if (k != j) {   // if a[j] is already the smallest we don't do this
            temp = a[k];
            a[k] = a[j];
            a[j] = temp;
        }
    }
}