1020 Tree Traversals (25分)

Suppose that all the keys in a binary tree are distinct positive integers. Given the postorder and inorder traversal sequences, you are supposed to output the level order traversal sequence of the corresponding binary tree.

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 postorder sequence and the third line gives the inorder sequence. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print in one line the level order traversal sequence of the corresponding binary tree. 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:

7
2 3 1 5 7 6 4
1 2 3 4 5 6 7

Sample Output:

4 1 6 3 5 7 2

思路：

由后序和中序即可唯一确定一棵树。树结构采用顺序结构，Tree[i]中存放i结点的左右孩子下标（空则为-1）.
每次递归调用，找出后序遍历序列的最后一个元素，该元素即为该子树的根节点，随后在中序序列找到该元素下标，从而确定根节点左右子树序列长度，递归遍历左右子树。边递归边建树。最后层序遍历即可。

源码：

#include<bits/stdc++.h>
#define Max 31
using namespace std;
int post[Max];
int in[Max];
vector<int> Tree[Max];
int Tree_travel(const int* post,const int* in,int length)
{
    if(length==0)
        return -1;
    int t=*(post+length-1);
    int i;
    for(i=0;i<length;i++)
    {
        //找到根节点在中序序列中的下标i
        if(in[i]==t)
            break;
    }
    //递归遍历左右子树，找出左右子树根节点
    int left=Tree_travel(post,in,i);
    int right=Tree_travel(post+i,in+i+1,length-i-1);
    //建树
    Tree[t].push_back(left);
    Tree[t].push_back(right);

    return t;
}
int main()
{
    int n;cin>>n;
    for(int i=0;i<n;i++)
        cin>>post[i];
    for(int i=0;i<n;i++)
        cin>>in[i];

    int root=Tree_travel(post,in,n);
    cout<<root;
    //层序遍历
    queue<int> que;
    que.push(Tree[root][0]);
    que.push(Tree[root][1]);
    while(!que.empty())
    {
        int t=que.front();
        que.pop();
        if(t!=-1)
        {
            cout<<" "<<t;
            que.push(Tree[t][0]);
            que.push(Tree[t][1]);
        }
    }
}

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旱地摸鱼(^･ｪ･^) 发布了97 篇原创文章 · 获赞 12 · 访问量 2384 私信 关注

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来源： https://blog.csdn.net/weixin_43301333/article/details/104098362