1086. Tree Traversals Again

1086. Tree Traversals Again (25)

时间限制

200 ms

内存限制

65536 kB

代码长度限制

16000 B

判题程序

Standard

作者

CHEN, Yue

An inorder binary tree traversal can be implemented in a non-recursive way with a stack. For example, suppose that when a 6-node binary tree (with the keys numbered from 1 to 6) is traversed, the stack operations are: push(1); push(2); push(3); pop(); pop();
push(4); pop(); pop(); push(5); push(6); pop(); pop(). Then a unique binary tree (shown in Figure 1) can be generated from this sequence of operations. Your task is to give the postorder traversal sequence of this tree.



Figure 1

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer N (<=30) which is the total number of nodes in a tree (and hence the nodes are numbered from 1 to N). Then 2N lines follow, each describes a stack operation in
the format: "Push X" where X is the index of the node being pushed onto the stack; or "Pop" meaning to pop one node from the stack.

Output Specification:

For each test case, print the postorder traversal sequence of the corresponding tree in one line. A solution is guaranteed to exist. All the numbers must be separated by exactly one space, and there must be no extra space at the end of the line.
Sample Input:

6
Push 1
Push 2
Push 3
Pop
Pop
Push 4
Pop
Pop
Push 5
Push 6
Pop
Pop

考查：二叉树的遍历，递归与非递归形式

#include<stdio.h>
#include<iostream>
#include<stack>
#include<string>
using namespace std;

struct Node
{
int data;
Node *lchild;
Node *rchild;
Node(int num):data(num), lchild(NULL), rchild(NULL){}
Node():lchild(NULL), rchild(NULL){}
};

Node* createTree(int n)
{
stack<Node*> s;
Node * ret = new Node();

string str_tmp;
cin>>str_tmp;
int i_tmp;
cin>>i_tmp;
ret->data = i_tmp;

Node* cur_node = ret;
s.push(ret);

while(-- n)
{
string type;
cin>>type;

if(type == "Push")
{
int num_push;
cin>>num_push;

Node *new_node = new Node(num_push);
if(cur_node->lchild == NULL)
cur_node->lchild = new_node;
else
cur_node->rchild = new_node;
s.push(new_node);
cur_node = new_node;
}
else if(type == "Pop")
{
cur_node = s.top();
s.pop();
}
}
return ret;
}

void postOrder(Node *root)
{
if(root->lchild != NULL)
postOrder(root->lchild);
if(root->rchild != NULL)
postOrder(root->rchild);
static bool flag = true;

if(flag)
{
cout<<root->data;
flag = false;
}
else
cout<<" "<<root->data;
}

int main()
{
freopen("F://Temp/input.txt", "r", stdin);
int n;
cin>>n;

if(n == 0)
return 0;
Node *root = createTree(2*n);
postOrder(root);

return 0;
}

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