PAT 1020

1020. Tree Traversals (25)

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

这题也不难，由后序跟中序序列构建一颗树，然后以层次遍历的方法输出各节点数据，主要输出后要把树给销毁，不然会造成内存泄露。
代码

 #include <stdio.h>
 #include <stdlib.h>

 typedef struct Node{
     int data;
     struct Node *left,*right;
 }Node;
 int postOrder[];
 int inOrder[];
 Node* buildTree(int,int,int,int);
 void printAndDestroyTree(Node *);
 int main()
 {
     int N,i;
     while(scanf("%d",&N) != EOF){
         for(i=;i<N;++i){
             scanf("%d",&postOrder[i]);
         }
         for(i=;i<N;++i){
             scanf("%d",&inOrder[i]);
         }
         Node *tree = buildTree(,N-,,N-);
         printAndDestroyTree(tree);
     }
     return ;
 }

 Node* buildTree(int postStart,int postEnd,int inStart,int inEnd)
 {
     if(postStart == postEnd){
         Node *p = (Node *)malloc(sizeof(Node));
         p->data = postOrder[postStart];
         p->left = p->right = NULL;
         return p;
     }
     else{
         Node *p = (Node *)malloc(sizeof(Node));
         p->data = postOrder[postEnd];
         p->left = p->right = NULL;
         int i = inStart;
         while(i<=inEnd && postOrder[postEnd] != inOrder[i++]);
         if(i > inStart+)
             p->left =  buildTree(postStart,postStart+i-inStart-,inStart,i-);
         if(i <= inEnd)
             p->right = buildTree(postStart+i-inStart-,postEnd-,i,inEnd);
         return p;
     }
 }

 void printAndDestroyTree(Node *p)
 {
     if(!p)
         return;
     Node *nodeArray[];
     int top=,base=;
     Node *q;
     nodeArray[top++] = p;
     while(top>base){
         q = nodeArray[base++];
         if(base == )
             printf("%d",q->data);
         else
             printf(" %d",q->data);
         if(q->left)
             nodeArray[top++] = q->left;
         if(q->right)
             nodeArray[top++] = q->right;
         free(q);
     }
     printf("\n");
 }