Sleeping_Zky 于 2017.09.01 21:31 提问

PAT甲级 1086. Tree Traversals Again 有测试点一直过不了，求帮助！

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
Sample Output:
3 4 2 6 5 1

#include
#include
#include
#include

using namespace std;

#define maxn 35

int NUM;
int n[maxn];
int index;

struct Node
{
int data;
Node* lchild;
Node* rchild;
}node;

Node* create()
{
if(n[index]==-1)
{
index++;
return NULL;
}
if(index>=2*NUM)
return NULL;
Node* root =new Node;
root->data=n[index];
root->lchild=root->rchild=NULL;
index++;
root->lchild=create();
root->rchild=create();
return root;
}

void postorder(Node* root)
{
if(root==NULL)
return;
postorder(root->lchild);
postorder(root->rchild);
printf("%d",root->data);
if(index+1!=NUM)
printf(" ");
index++;
}

int main()
{
scanf("%d",&NUM);
string word;
for(int i=0;i {
cin>>word;
if(word=="Push")
cin>>n[i];
if(word=="Pop")
n[i]=-1;
}
Node * root;
root =create();
index=0;
postorder(root);
return 0;
}

1个回答

caozhy      2017.09.01 23:54