算法导论学习笔记（1）

一. 插入排序算法

伪码:INSERTION-SORT(A)

1. for j = 2 to A.length

2.      key = A[j]

3.      //Insert A[j] into the sorted sequence  A[1..j-1]

4.      i = j -1

5.      while i > 0 and A[i] > key

6.               A[i +1] = A[i]

7.               i = i -1

8.      A[i +1] = key

代码实现：

#include<iostream>
using namespace std;
void insertion_sort(int *arry,int length)
{
	for(int j = 1; j < length; j++)
	{
		int key = arry[j];
		//insert a[j] into the sorted sequence a[0...j-1]
		int i = j-1;
		while(i >= 0 && arry[i] > key)
		{
			arry[i+1] = arry[i];
			i = i -1;
		}
		arry[i+1] = key;
	}
}
int main()
{
	int a[6] = {5,2,4,6,1,3};
	insertion_sort(a,6);
	for(int i = 0; i < 6; i++)
		cout << a[i] << " ";
	cout << endl;
}

二.选择算法（练习2.2-2）

SELECTION -SORT(A)
1. n = A.length
2. for j = 1 to n 1
3.     smallest = j
4.      for i = j + 1 to n
5.           if A[i] < A[smallest]
6.              smallest = i
7. exchange A[j]  with A[smallest]

代码实现：

#include<iostream>
using namespace std;
void swap(int& a, int &b)
{
	int index = a;
	a = b;
	b= index;
}
void selection_sort(int* arry, int length)
{
	for (int j = 0; j < length-1; j++)
	{
		int smallest = j;
		for (int i = j+1; i < length; i++)
			if(arry[i] < arry[smallest])
				smallest = i;
		swap(arry[j], arry[smallest]);
	}
}
int main()
{
	int a[6] = {5,2,4,6,1,3};
	selection_sort(a, 6);
	for(int i = 0; i < 6; i++)
		cout << a[i] << " ";
	cout << endl;
	return 0;
}