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[30];
int inOrder[30];
Node* buildTree(int,int,int,int);
void printAndDestroyTree(Node *);
int main()
{
    int N,i;
    while(scanf("%d",&N) != EOF){
        for(i=0;i<N;++i){
            scanf("%d",&postOrder[i]);
        }
        for(i=0;i<N;++i){
            scanf("%d",&inOrder[i]);
        }
        Node *tree = buildTree(0,N-1,0,N-1);
        printAndDestroyTree(tree);
    }
    return 0;
}

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+1)
            p->left =  buildTree(postStart,postStart+i-inStart-2,inStart,i-2);
        if(i <= inEnd)
            p->right = buildTree(postStart+i-inStart-1,postEnd-1,i,inEnd);
        return p;
    }
}

void printAndDestroyTree(Node *p)
{
    if(!p)
        return;
    Node *nodeArray[30];
    int top=0,base=0;
    Node *q;
    nodeArray[top++] = p;
    while(top>base){
        q = nodeArray[base++];
        if(base == 1)
            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("
");
}