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;

}

}

}