LearnHowToThink

一、BubbleSort and XListview

1、BubbleSort

（1）analysis

traverse、compare、exchange、cycle、optimize strategy

loop outside times n-1

loop inside times n-i-1 it reduces 1 next cycle

（2）code：

void BubbleSort(int arr[],int n)
{
    int i,j,temp;
    for(i=0;i<n-1;i++)
    {
        for(j=0;j<n-i-1;j++)
        {
            if(arr[j]>arr[j+1])
            {
                temp=arr[j];
                arr[j]=arr[j+1];
                arr[j+1]=temp;
            }
        }
    }
}

（3）price：o(n*n)

（4）optimize strategy

no exchange，then break：

void BubbleSort2(int arr[],int n)
{
    int i,j,temp,flag;
    for(i=0;i<n-1;i++)
    {
        flag=0;
        for(j=0;j<n-i-1;j++)
        {
            if(arr[j]>arr[j+1])
            {
                temp=arr[j];
                arr[j]=arr[j+1];
                arr[j+1]=temp;
                flag=1;
            }
        }
        if(!flag)
        {
            break;
        }
    }
}

2、ChooseSort

（1）analysis

choose the min element every time，and exchange it with the first（move one by one） element。

（2）code

void ChooseSort(int arr[],int n)
{
    int i,j,temp,min;
    for(i=0;i<n-1;i++)
    {
        min=i;
        for(j=i+1;j<n;j++)
        {
            if(arr[j]<arr[min])
            {
                min=j;
            }
        }
        if(i!=min)
        {
            temp=arr[i];
            arr[i]=arr[min];
            arr[min]=temp;
        }
    }
}

（3）price：o(n*n)

（4）supplementary

Of course，you can also choose the max element to exchange。

 

3、InsertSort

analysis：

     Insert a number into a list which is already ordered。traverse the list from the tail to the head until  it is larger than current and find where to place the number。

code：

void InsertSort(int a[],int n)
{
    int i,j;
    for(i=0;i<n-1;i++)
    {
        int m=a[i+1];
        for(j=i+1;j>0;j--)
        {
            if(m<a[j-1])
            {
                a[j]=a[j-1];
            }
            else
            {
                break;//这一句非常关键
            }
        }
        a[j]=m;
    }
}

 

二、XListView

1、layout、arrow、textview，header and footer is different

2、three conditions，normal、ready、refreshing，different condition has different layout，vary from one to one.

3、event handle

when trigger the event and what to do.

4、XlistViewHeader XListViewFooter XListView XListViewActivity

related api：LinearLayout、ListView、activity、OnScrollListener