算法9：在一个循环有序的数组里查找一个数

解题思路

采用中分方法进行查找，考虑到是循环有序的数组，存在一边有序的情况，将中间值与最左边值比较，查看是否有序，则左有序，否则就是右有序。然后再确定待查找值的区域。

c++代码

//loopBuffer:循环有序数组//length：循环有序数组长度//value：待查找的数//return:返回待查找数在数组中的位置int BinarySearch(int* loopBuffer,int length, int value){    if(loopBuffer == NULL || length == 0)    {        cout<<"buffer is error"<<endl;        return -1;    }    int left = 0;    int right = length -1;    int mid = (left+right)/2;    while(left <= right)    {        mid = (left+right)/2;        if(value == loopBuffer[mid])        {            return mid;        }        if(loopBuffer[left]<loopBuffer[mid])//左有序        {            if(loopBuffer[left]<= value && value <= loopBuffer[mid])            {                right = mid - 1;            }            else            {                left = mid +1;            }        }        else //右有序        {            if(loopBuffer[mid] <= value && value <= loopBuffer[right])            {                left = mid+1;            }            else            {                right = mid-1;            }        }    }    return -1;}

测试代码

int _tmain(int argc, _TCHAR* argv[]){    int loopBuffer[10] = {6,7,8,9,0,1,2,3,4,5};    int i = 0;    int value = 0;    while(i < 10)    {        cout<<"please input a value in {6,7,8,9,0,1,2,3,4,5}:"<<endl;        cin>>value;        cout<<"pos = "<<BinarySearch(loopBuffer,10,value)<<endl;        i++;    }    cout<<"please input a value not in {6,7,8,9,0,1,2,3,4,5}:"<<endl;    cin>>value;    cout<<"pos = "<<BinarySearch(loopBuffer,10,value)<<endl;    return 0;}