算法之二分查找

二分查找思想：

1、数组从小到大排序；2、查找的key每次和中间数比较，如果key小于mid ，查找mid左侧的数组部分；如果key大于mid，则查找mid右侧的数组部分；如果相等，则直接返回mid

 

//非递归查找
int BinarySearch(int *array, int aSize, int key)
{
    if ( array == NULL || aSize == 0 )
        return -1;
    int low = 0;
    int high = aSize - 1;
    int mid = 0;

 

   while ( low <= high )
    {
mid = (low + high )/2;

if ( array[mid] < key)
low = mid + 1;
else if ( array[mid] > key )
high = mid - 1;
else
return mid;
}
return -1;
}
//递归
int BinarySearchRecursive(int *array, int low, int high, int key)
{
if ( low > high )
return -1;
int mid = ( low + high )/2;

if ( array[mid] == key )
return mid;
else if ( array[mid] < key )
return BinarySearchRecursive(array, mid+1, high, key);
else
return BinarySearchRecursive(array, low, mid-1, key);
}

 

int main()
{
int array[10];
for (int i=0; i<10; i++)
array[i] = i;

 

cout<<"No recursive:"<<endl;
cout<<"position:"<<BinarySearch(array, 10, 6)<<endl;
cout<<"recursive:"<<endl;
cout<<"position:"<<BinarySearchRecursive(array, 0, 9, 6)<<endl;

 

return 0;
}