PAT_A1020#Tree Traversals

Source:

PAT A1020 Tree Traversals (25 分)

Description:

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

Keys:

• 二叉树的建立和遍历

Code:

 /*
 time: 2019-06-30 14:40:45
 problem: PAT_A1020#Tree Traversals
 AC: 08:33

 题目大意：
 给出后序和中序遍历，打印层序遍历
 */
 #include<cstdio>
 #include<queue>
 using namespace std;
 const int M=;
 int post[M],in[M],n;
 struct node
 {
     int data;
     node *lchild,*rchild;
 };

 node *Create(int postL, int postR, int inL, int inR)
 {
     if(postL > postR)
         return NULL;
     node *root = new node;
     root->data = post[postR];
     int k;
     for(k=inL; k<=inR; k++)
         if(in[k] == post[postR])
             break;
     int numLeft = k-inL;
     root->lchild = Create(postL,postL+numLeft-,inL,k-);
     root->rchild = Create(postL+numLeft,postR-,k+,inR);
     return root;
 }

 void LayerOrder(node *root)
 {
     queue<node*> q;
     q.push(root);
     int pt=;
     while(!q.empty())
     {
         root = q.front();
         q.pop();
         printf("%d%c", root->data, ++pt==n?'\n':' ');
         if(root->lchild)
             q.push(root->lchild);
         if(root->rchild)
             q.push(root->rchild);
     }
 }

 int main()
 {
 #ifdef ONLINE_JUDGE
 #else
     freopen("Test.txt", "r", stdin);
 #endif // ONLINE_JUDGE

     scanf("%d", &n);
     for(int i=; i<n; i++)
         scanf("%d", &post[i]);
     for(int i=; i<n; i++)
         scanf("%d", &in[i]);
     node *root = Create(,n-,,n-);
     LayerOrder(root);

     return ;
 }