最常见的程序员面试题(2)二叉树逐层打印

二叉树的遍历都不能逐层访问。考虑用一个FIFO队列: 压入树根，然后:

(1) 每次取出一个节点，打印数据。压入节点的左右子树

(2) 删除队列头节点。

(3) 循环(1)-(2)直到队列为空。

用C++和Java分别实现。

[cpp] view plaincopyprint?

1. #include <deque>   
2. struct node{  
3.     explicit node( int d )  
4.         : data( d ), pLeft( nullptr ), pRight( nullptr )  
5.     {}  
6.     ~node(){  
7.         delete pLeft;  
8.         delete pRight;  
9.     }  
10.     int data;  
11.     node* pLeft;  
12.     node* pRight;  
13.     node* appendLeft( node* pn ){  
14.         if( pLeft )delete pLeft;  
15.         pLeft = pn;  
16.         return pLeft;  
17.     }  
18.     node* appendRight( node* pn ){  
19.         if( pRight )delete pRight;  
20.         pRight = pn;  
21.         return pRight;  
22.     }  
23. };  
24. void printLayers( node& n ){  
25.     std::deque<node*> di;  
26.     di.push_back(&n);  
27.     while(di.size()){  
28.         node* pn=di.front();  
29.         printf("%d,",pn->data);  
30.         if(pn->pLeft) di.push_back(pn->pLeft);  
31.         if(pn->pRight)di.push_back(pn->pRight);  
32.         di.pop_front();  
33.     }  
34. }  
35. int main(void){  
36.     node root(1);  
37.     node* r_left=root.appendLeft( new node(2) );  
38.     node* r_right=root.appendRight( new node(3) );  
39.     node* lr=r_left->appendRight( new node(5) );  
40.     node* ll=r_left->appendLeft( new node(4) );  
41.     node* rl=r_right->appendLeft( new node(6) );  
42.     node* rr=r_right->appendRight( new node(7) );  
43.     printLayers( root );  
44.     return 0;  
45. }  

#include <deque>struct node{    explicit node( int d )        : data( d ), pLeft( nullptr ), pRight( nullptr )    {}    ~node(){        delete pLeft;        delete pRight;    }    int data;    node* pLeft;    node* pRight;    node* appendLeft( node* pn ){        if( pLeft )delete pLeft;        pLeft = pn;        return pLeft;    }    node* appendRight( node* pn ){        if( pRight )delete pRight;        pRight = pn;        return pRight;    }};void printLayers( node& n ){    std::deque<node*> di;    di.push_back(&n);    while(di.size()){        node* pn=di.front();        printf("%d,",pn->data);        if(pn->pLeft) di.push_back(pn->pLeft);        if(pn->pRight)di.push_back(pn->pRight);        di.pop_front();    }}int main(void){    node root(1);    node* r_left=root.appendLeft( new node(2) );    node* r_right=root.appendRight( new node(3) );    node* lr=r_left->appendRight( new node(5) );    node* ll=r_left->appendLeft( new node(4) );    node* rl=r_right->appendLeft( new node(6) );    node* rr=r_right->appendRight( new node(7) );    printLayers( root );    return 0;}

[java] view plaincopyprint?

1. import java.util.*;  
2. public class Revert {  
3.     public static void main(String[] args) {  
4.         node root=new node(1);  
5.         node r=root.appendRight(new node(3));  
6.         node l=root.appendLeft(new node(2));  
7.         r.appendLeft(new node(6));  
8.         r.appendRight(new node(7));  
9.         l.appendRight(new node(5));  
10.         l.appendLeft(new node(4));  
11.         Revert.printLayer( root );  
12.     }  
13.     static class node{  
14.         int data;  
15.         node left;  
16.         node right;  
17.         node( int d ){  
18.             data = d;  
19.             left = null;  
20.             right = null;  
21.         }  
22.         node appendLeft( node pn ){  
23.             left = pn;  
24.             return left;  
25.         }  
26.         node appendRight( node pn ){  
27.             right = pn;  
28.             return right;  
29.         }  
30.     }  
31.     static void printLayer( node root ){  
32.         LinkedList<node> li=new LinkedList<node>();  
33.         li.push( root );  
34.         while( li.size() != 0 ){  
35.             node n=li.peekFirst();  
36.             System.out.println(","+n.data);  
37.             if(n.left !=null)li.addLast(n.left);  
38.             if(n.right!=null)li.addLast(n.right);  
39.             li.removeFirst();  
40.         }  
41.     }  
42. }  

import java.util.*;public class Revert {public static void main(String[] args) {node root=new node(1);node r=root.appendRight(new node(3));node l=root.appendLeft(new node(2));r.appendLeft(new node(6));r.appendRight(new node(7));l.appendRight(new node(5));l.appendLeft(new node(4));Revert.printLayer( root );}static class node{int data;node left;node right;node( int d ){data = d;left = null;right = null;}node appendLeft( node pn ){left = pn;return left;}node appendRight( node pn ){right = pn;return right;}}static void printLayer( node root ){LinkedList<node> li=new LinkedList<node>();li.push( root );while( li.size() != 0 ){node n=li.peekFirst();System.out.println(","+n.data);if(n.left !=null)li.addLast(n.left);if(n.right!=null)li.addLast(n.right);li.removeFirst();}}}