二分查找

Position BinarySearch( List L, ElementType X )
{
    int left = 1, right = L->Last;
    int mid;
    while(left <= right)
    {
        mid = (left + right) / 2;
        if(L->Data[mid] > X)    //X在左侧
            right = mid - 1;    
        else if(L->Data[mid] < X)  //X在右侧
            left = mid + 1;
        else 
            return mid;         //X==L->Data[mid] 
    }
    return NotFound;     //没找到
}