数组生成MaxTree——C++

MaxTree

`class node
{
　public:
int value;
node()
{
　left = NULL;
　right = NULL;
　　  }
　~node(){};
　　  node( int val )
　{
value = val;
left = NULL;
right = NULL;
　}
　node *left,*right;
};
node* maxTree( int* array,int length ,node* nArr)
{
if ( !array || length<=0)
　{
　   return NULL;
　}
nArr = new node[length];
　for (int i = 0 ; i < length; i++)
　{
nArr[i] = node(array[i]);
　}

node** leftmax = new node*[length];
node** rightmax = new node*[length];

// 左边最近、最大的值
std::stack<node*> nstack;
for ( int i =0; i < length; i++ )
{
while ( !nstack.empty() )
{
if ( nArr[i].value >= nstack.top()->value )
{
nstack.pop();
}
else
{
leftmax[i] = nstack.top();
break;
}
}
if ( nstack.empty() )
{
leftmax[i] = NULL;
}
nstack.push(&nArr[i]);
}

while ( !nstack.empty() )
{
nstack.pop();
}
// 右边最近、最大的值
for ( int i =length-1; i >= 0; i-- )
{
while ( !nstack.empty() )
{
if ( nArr[i].value >= nstack.top()->value )
{
nstack.pop();
}
else
{
node temp = *nstack.top();
rightmax[i] = nstack.top();
break;
}
}
if ( nstack.empty() )
{
rightmax[i] = NULL;
}

nstack.push(&nArr[i]);
}

//建立树
node* head;
for ( int i = 0; i < length; i++ )
{
if ( !leftmax[i] && !rightmax[i] )//左右两边都没有最大值
{
head = &nArr[i];
}
else if ( !leftmax[i] )//最大值在右边
{

if ( !rightmax[i]->left )
rightmax[i]->left = &nArr[i];
else
rightmax[i]->right = &nArr[i];
}
else if ( !rightmax[i] )//最大值在左边
{
if ( !leftmax[i]->left )
leftmax[i]->left = &nArr[i];
else
leftmax[i]->right = &nArr[i];
}
else //左右都有最大值，比较那个值小
{
node* parent = (leftmax[i]->value > rightmax[i]->value)? rightmax[i] : leftmax[i];
if ( !parent->left )
{
parent->left = &nArr[i];
}
else
{
parent->right = &nArr[i];
}
}
}
delete [] leftmax;
delete [] rightmax;
return head;
}`