PAT 1020

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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:

72 3 1 5 7 6 41 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

 1 #include <stdio.h> 2 #include <stdlib.h> 3  4 typedef struct Node{ 5     int data; 6     struct Node *left,*right; 7 }Node; 8 int postOrder[30]; 9 int inOrder[30];10 Node* buildTree(int,int,int,int);11 void printAndDestroyTree(Node *);12 int main()13 {14     int N,i;15     while(scanf("%d",&N) != EOF){16         for(i=0;i<N;++i){17             scanf("%d",&postOrder[i]);18         }19         for(i=0;i<N;++i){20             scanf("%d",&inOrder[i]);21         }22         Node *tree = buildTree(0,N-1,0,N-1);23         printAndDestroyTree(tree);24     }25     return 0;26 }27 28 Node* buildTree(int postStart,int postEnd,int inStart,int inEnd)29 {30     if(postStart == postEnd){31         Node *p = (Node *)malloc(sizeof(Node));32         p->data = postOrder[postStart];33         p->left = p->right = NULL;34         return p;35     }36     else{37         Node *p = (Node *)malloc(sizeof(Node));38         p->data = postOrder[postEnd];39         p->left = p->right = NULL;40         int i = inStart;41         while(i<=inEnd && postOrder[postEnd] != inOrder[i++]);42         if(i > inStart+1)43             p->left =  buildTree(postStart,postStart+i-inStart-2,inStart,i-2);44         if(i <= inEnd)45             p->right = buildTree(postStart+i-inStart-1,postEnd-1,i,inEnd);46         return p;47     }48 }49 50 void printAndDestroyTree(Node *p)51 {52     if(!p)53         return;54     Node *nodeArray[30];55     int top=0,base=0;56     Node *q;57     nodeArray[top++] = p;58     while(top>base){59         q = nodeArray[base++];60         if(base == 1)61             printf("%d",q->data);62         else63             printf(" %d",q->data);64         if(q->left)65             nodeArray[top++] = q->left;66         if(q->right)67             nodeArray[top++] = q->right;68         free(q);69     }70     printf("\n");71 }

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