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 (≤), 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

建树，然后层序遍历就是

#include<iostream>
#include<vector>
#include<queue>

using namespace std;

vector<int> post,in,ans;
int n;//总的节点数
struct node
{
    int key;
    node* left;
    node* right;
};

node* buildtree(node* root,int inleft,int inright,int postleft,int postright)
{
    if(inleft>inright)//左边界大于右边界则返回空
        return NULL;
    int i = inleft;//i从中序遍历的左边界开始

    while(in[i]!=post[postright])//寻找根节点在中序遍历的下标
        i++;
//跳出while循环时，i是中序遍历的根节点下标

    if(root==NULL)
    {
        root = new node();
        root->key = in[i];
        root->left = NULL;
        root->right = NULL;
    }

    root->left = buildtree(root->left,inleft,i-1,postleft,postleft+(i-inleft-1));//递归构造左子树   （i-inleft-1）表示中序遍历左子树的的元素一共多少个， -1表示减去根节点
    root->right = buildtree(root->right,i+1,inright,postleft+(i-inleft),postright-1);

    return root;
}

void level(node* root)
{
    queue<node*> q;
    q.push(root);
    while(!q.empty())
    {
        node* temp = q.front();//temp指向队头元素
        q.pop();//出队
        ans.push_back(temp->key);//层序遍历的结果放在ans中
        if(temp->left!=NULL)//左子树入队
            q.push(temp->left);
        if(temp->right!=NULL)//右子树入队
            q.push(temp->right);
    }
}

int main()
{
    cin>>n;
    post.resize(n);
    in.resize(n);
    for(int i=0;i<n;i++)
        cin>>post[i];
    for(int i=0;i<n;i++)
        cin>>in[i];

    node* tree = NULL;
    tree = buildtree(tree,0,n-1,0,n-1);
    level(tree);
    for(int i=0;i<ans.size();i++)
    {
        cout<<ans[i];
        if(i!=ans.size()-1)
            cout<<" ";
    }

    return 0;
}