昨天同学去參加阿里巴巴面试，被问到二叉树的一些基本问题，分享一下：
1.怎样非递归dfs求得树的深度
2.怎样非递归bfs求得树的深度
*3.怎样非递归地中前后序遍历二叉查找树。
二叉树写过不下十次了。可是基本每次都是用递归来写。一时间问道还不能一下写出来。
问题二还是比較好写，一的话可能须要细致想想，可是假如是面试的话。可能我一时也说不出来。
老实说，我自己写得代码总得看来是满长的。可是局部核心的是相对照较好理解的。
/***********************************************************
> OS : Linux 3.13.0-24-generic (Mint-17)
> Author : yaolong
> Mail : dengyaolong@yeah.net
> Time : 2014年09月18日 星期四 12时24分57秒
**********************************************************/
#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>
#include <stack>
#include <queue>
#include <cstdlib>
using namespace std;
template<typename Comparable>
class BinarySearchTree
{
public:
BinarySearchTree()
{
root = NULL;
};
void insert ( Comparable x ) //非递归插入
{
if ( root == NULL ) //由于不是传引用指针
{
root = new Node ( x );
}
else
{
insert ( x, root );
}
}
bool contains ( Comparable x ) //递归查询
{
return contains ( x, root );
}
void travel_in() //非递归中序遍历
{
travel_in ( root );
}
void travel_dg_in() //递归中序遍历
{
travel_dg_in ( root );
}
void travel_pre() //非递归前序遍历
{
travel_pre ( root );
}
void travel_dg_pre() //递归前序遍历
{
travel_dg_pre ( root );
}
void travel_suf() //非递归后序遍历，略微难
{
travel_suf ( root );
}
void travel_dg_suf() //递归后序遍历
{
travel_dg_suf ( root );
}
int get_depth_dg() //递归搜索树的深度
{
return get_depth_dg ( root );
}
int get_depth_dfs() //非递归，深度搜索树的深度
{
return get_depth_dfs ( root );
}
int get_depth_bfs() //非递归。宽度搜索树得深度
{
return get_depth_bfs ( root );
}
private:
class Node
{
public:
Comparable element;
Node *left;
Node *right;
Node ( Comparable e , Node *l = NULL, Node *r = NULL ) : element ( e ), left ( l ), right ( r )
{
}
};
void insert ( Comparable x, Node *p )
{
while ( 1 )
{
if ( x > p->element ) //比当前节点元素大。插入到右边
{
if ( p->right == NULL )
{
p->right = new Node ( x );
return;
}
p = p->right;
}
else if ( x < p->element )
{
if ( p->left == NULL )
{
p->left = new Node ( x );
return;
}
p = p->left;
}
else
{
//nothing to do
return;
}
}
}
bool contains ( Comparable x, Node *p )
{
while ( p != NULL )
{
if ( x > p->element )
{
p = p->right;
}
else if ( x < p->element )
{
p = p->left;
}
else
{
return 1;
}
}
return 0;
}
void travel_pre ( Node *p ) //前序遍历
{
stack<Node *> stk;
while ( p != NULL || !stk.empty() )
{
while ( p != NULL ) //先读。再往左。知道叶子
{
cout << p->element << " ";
stk.push ( p );
p = p->left;
}
if ( !stk.empty() ) //左路訪问完，退回訪问右路，即用右儿子进行继续递归，进行前序遍历
{
p = stk.top();
stk.pop();
p = p->right;
}
}
}
void travel_dg_pre ( Node *p )
{
if ( p == NULL )
{
return;
}
cout << p->element << " ";
travel_dg_pre ( p->left );
travel_dg_pre ( p->right );
}
void travel_in ( Node *p )
{
stack<Node *> stk;
while ( p != NULL || !stk.empty() )
{
while ( p != NULL )
{
stk.push ( p );
p = p->left;
}
if ( !stk.empty() )
{
p = stk.top();
stk.pop();
cout << p->element << " ";
p = p->right;
}
}
}
void travel_dg_in ( Node *p )
{
if ( p == NULL )
{
return;
}
travel_dg_in ( p->left );
cout << p->element << " ";
travel_dg_in ( p->right );
}
void travel_suf ( Node *p )
{
stack<Node *> stk;
Node *prev = NULL;
while ( p != NULL || !stk.empty() )
{
while ( p != NULL )
{
stk.push ( p );
p = p->left;
}
p = stk.top();
if ( p->right == NULL || p->right == prev )
{
cout << p->element << " ";
prev = p;
stk.pop();
p = NULL;
}
else
{
p = p->right;
}
}
}
void travel_dg_suf ( Node *p )
{
if ( p == NULL )
{
return;
}
travel_dg_suf ( p->left );
travel_dg_suf ( p->right );
cout << p->element << " ";
}
int get_depth_dfs ( Node *p )
{
int depth = 0, d = 0;
stack<Node *> stk;
stack<int> stk_depth;
while ( p != NULL || !stk.empty() )
{
while ( p != NULL )
{
stk.push ( p );
stk_depth.push ( d++ );
p = p->left;
}
if ( !stk.empty() )
{
d = stk_depth.top();
depth = max ( d, depth );
p = stk.top();
stk.pop();
stk_depth.pop();
p = p->right;
d++;
}
}
return depth;
}
int get_depth_bfs ( Node *p )
{
queue<Node *> q;
queue<int> q_d;
int d = 0;
int depth = 0;
q.push ( p );
q_d.push ( d );
while ( !q.empty() )
{
p = q.front();
d = q_d.front() ;
++d;
q.pop();
q_d.pop();
if ( p->left != NULL )
{
q_d.push ( d ) ;
q.push ( p->left );
depth = max ( depth, d );
}
if ( p->right != NULL )
{
q_d.push ( d ) ;
q.push ( p->right );
depth = max ( depth, d );
}
}
return depth;
}
int get_depth_dg ( Node *p )
{
int depth = 0;
if ( p->left != NULL )
{
depth = max ( depth, get_depth_dg ( p->left ) + 1 );
}
if ( p->right != NULL )
{
depth = max ( depth, get_depth_dg ( p->right ) + 1 );
}
return depth;
}
Node *root;
};
int main()
{
BinarySearchTree<int> t;
for ( int i = 0; i < 100; i++ )
{
int tmp = random() % 100000;
//cout<<tmp;
t.insert ( tmp );
}
cout << "Insert OK" << endl;
cout << t.contains ( 4 ) << endl;
cout << t.contains ( 2 ) << endl;
cout << "非递归递归前序遍历:
";
t.travel_pre();
cout << "
递归前序遍历
";
t.travel_dg_pre();
cout << "
递归中序遍历
";
t.travel_dg_in();
cout << "
非递归递归中序遍历:
";
t.travel_in();
cout << "
递归后序遍历
";
t.travel_dg_suf();
cout << "
非递归递归后序遍历:
";
t.travel_suf();
cout << "
递归求的树的高度
";
cout << t.get_depth_dg();
cout << "
非递归dfs求的树的高度
";
cout << t.get_depth_dfs();
cout << "
非递归bfs求的树的高度
";
cout << t.get_depth_bfs();
}