快速排序与二分查找

#include <iostream>
#include <string>
using namespace std;

void quicksort(int arry[], int low, int high)
{
    if(low >= high)
        return;

    int l = low;
    int h = high;
    int key = arry[l];

    while(l < h)
    {
        while(l < h && key < arry[h]){ --h; }
        if(l < h)
        {
            arry[l++] = arry[h];
        }
        while(l < h && key > arry[l]){ ++l; }
        if(l < h)
        {
            arry[h--] = arry[l];
        }
    }
    arry[l] = key;

    quicksort(arry, low, l - 1);
    quicksort(arry, l + 1, high);
}

bool binarysearch(int arry[], int n, int low, int high, int &key, int &index)
{
    if(low > n - 1 || high < 0 || low > high)
    {
        cout<<"can't find "<<key<<endl;
        return false;
    }
    int middle = (low + high) % 2 == 0 ? (low + high) / 2 : (low + high) / 2 + 1;
    if(arry[middle] == key)
    {
        index = middle;
        return true;
    }
    else
    {
        if(arry[middle] > key) high = middle - 1;
        if(arry[middle] < key) low = middle + 1;
    }

    return binarysearch(arry, n, low, high, key, index);
}

int main()
{
    int arry[] = {1,2,6,7,854,23,4,22,44,55};
    int size = sizeof(arry)/sizeof(arry[0]);
    quicksort(arry, 0, size -1);
    cout<<"arry size is "<<size<<", after sort is:"<<endl;
    for(int i = 0; i < size; ++i)
    {
        cout<<arry[i]<<",";
    }
    cout<<endl;
    cout<<"binarysearch test."<<endl;
    int index;
    int value = 854;
    if(binarysearch(arry, size, 0, size - 1, value, index))
    {
        cout<<"find "<<value<<" ok, index is "<<index<<endl;
    }
    value = 54;
    if(binarysearch(arry, size, 0, size - 1, value, index))
    {
        cout<<"find "<<value<<" ok, index is "<<index<<endl;
    }

    return 0;
}

 

2 2 4 9 3 6 7 1 5 首先用2当作基准，使用i j两个指针分别从两边进行扫描，把比2小的元素和比2大的元素分开。首先比较2和5，5比2大，j左移

2 2 4 9 3 6 7 1 5 比较2和1，1小于2，所以把1放在2的位置

2 1 4 9 3 6 7 1 5 比较2和4，4大于2，因此将4移动到后面

2 1 4 9 3 6 7 4 5 比较2和7，2和6，2和3，2和9，全部大于2，满足条件，因此不变

经过第一轮的快速排序，元素变为下面的样子

[1] 2 [4 9 3 6 7 5]