PAT 甲级 1127 ZigZagging on a Tree (30 分) 二刷

Suppose that all the keys in a binary tree are distinct positive integers. A unique binary tree can be determined by a given pair of postorder and inorder traversal sequences. And it is a simple standard routine to print the numbers in level-order. However, if you think the problem is too simple, then you are too naive. This time you are supposed to print the numbers in “zigzagging order” – that is, starting from the root, print the numbers level-by-level, alternating between left to right and right to left. For example, for the following tree you must output: 1 11 5 8 17 12 20 15.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤30), the total number of nodes in the binary tree. The second line gives the inorder sequence and the third line gives the postorder sequence. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the zigzagging sequence of the tree in a line. All the numbers in a line must be separated by exactly one space, and there must be no extra space at the end of the line.

Sample Input:

8
12 11 20 17 1 15 8 5
12 20 17 11 15 8 5 1

Sample Output:

1 11 5 8 17 12 20 15

1、根据中序遍历和后续遍历建树，写了很多次了。
2、层次遍历，将每一次的结点放入对应的vector中存储。
3、格式化输出，根据层次的奇偶性。

#include <iostream>
#include <cstdio>
#include <queue>
#include <vector>
using namespace std;
struct node{
    int data;
    int level;
    node *lchild,*rchild;
};
int N;
int a[35];
int b[35];
vector<int> level[35];
int deep=0;
void creat_Tree(int l1,int r1,int l2,int r2,node* &t)
{
    if(l1>r1)
        return;
    t=new node;
    t->data=b[r2];
    t->lchild=NULL;
    t->rchild=NULL;
    int i;
    for(i=l1;i<=r1;i++)
        if(a[i]==b[r2])
            break;
    creat_Tree(l1,i-1,l2,l2+i-1-l1,t->lchild);
    creat_Tree(i+1,r1,l2+i-l1,r2-1,t->rchild);
}
void level_tra(node *root)
{
    if(root==NULL)
        return;
    root->level=1;
    queue<node*> que;
    que.push(root);
    while(!que.empty())
    {
        node *curr=que.front();
        que.pop();
        level[curr->level].push_back(curr->data);
        deep=curr->level;
        if(curr->lchild!=NULL)
        {
            curr->lchild->level=curr->level+1;
            que.push(curr->lchild);
        }
        if(curr->rchild!=NULL)
        {
            curr->rchild->level=curr->level+1;
            que.push(curr->rchild);
        }
    }
}
int main(){
    cin>>N;
    node *root=NULL;
    for(int i=1;i<=N;i++)
        scanf("%d",&a[i]);
    for(int i=1;i<=N;i++)
        scanf("%d",&b[i]);
    creat_Tree(1,N,1,N,root);
    level_tra(root);
    for(int i=1;i<=deep;i++)
    {
        if(i%2==0)
           for(int j=0;j<level[i].size();j++)
                if(i==deep&&j==level[i].size()-1)
                    printf("%d\n",level[i][j]);
                else
                    printf("%d ",level[i][j]);
        else
            for(int j=level[i].size()-1;j>=0;j--)
                if(i==deep&&j==0)
                    printf("%d\n",level[i][j]);
                else
                    printf("%d ",level[i][j]);
    }
    return 0;
}