排序算法之选择排序

选择排序是：选出A中最小的与A[1]进行交换（假设是升序），再选择次小的与A[2]交换，对A进行n-1次这样的过程。

算法伪代码如下：

for i-> to 1 length[A]-1
	do key<-a[i]
	j<-i+1
	n<-j
	while j<= length[A]
		if key>A[j]
			do key=A[j]
			n=j
		do j<-j+1
	A[n]<-A[i]
	A[i]<-key

 

算法时间分析

                                                                  运行时间       运行次数

for i-> to 1 length[A]-1                              c1                   n-1          do key<-a[i]                                          c2            n-1           j<-i+1                                                  c3           n-1           n<-i                                                    c4             n-1           while j<= length[A]                          c5          sum(ti)                  if key>A[j]                                    c6            sum(ti-1)                         do key=A[j]                                c7         sum(ti-2)                          n=j                                              c8         sum(ti-2)                   do j<-j+1                                           c9          sum(ti-1)          A[n]<-A[i]                                                  c10         n-1          A[i]<-key                                                     c11            n-1

   

其中i的取值为1 to n-1

运行次数*运行时间即可得到算法复杂度，可以看出，计算后的最高项为n^2，因此次算法复杂度为O(n^2)。

算法C++实现代码如下：

#include<iostream>
int main()
{
	int A[10]={5,3,1,7,9,2,6,4,10,8};
	for (int i=0;i<=8;i++)
	{
		int key=A[i];
		int j=i+1;
		int n=i;
		while (j<=9)
		{
			if (key<A[j])
			{
				key=A[j];
				n=j;
			}
			j++;
		}
		
			A[n]=A[i];
			A[i]=key;
		
	}
	return 0;
}