PAT 甲级 1020 Tree Traversals (25)（25 分）

1020 Tree Traversals (25)（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 (<=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

# include <iostream>
# include <queue>
using namespace std;
const int maxn = 1e5;

int n;
int pre[maxn], in[maxn], post[maxn];
struct node{
	int data; 
	node *lchild;
	node *rchild;
};

node* create_post_in(int postl, int postr, int inl, int inr){
	if(postl > postr)
		return NULL; 
	int k, numl;
	node *root = new node;
	root->data = post[postr];
	for(k = inl; k <= inr; k++){
		if(post[postr] == in[k])
			break;
	}
	numl = k - inl;
	root->lchild = create_post_in(postl, postl+numl-1, inl, k- 1);
	root->rchild = create_post_in(postl+numl, postr-1, k+1, inr);
	return root;
}
/*
node* create_pre_in(int prel, int prer, int inl, int inr){
	if(prel > prer) return NULL;
	int numl, k;
	node *root = new node;
	root->data = pre[prel];
	for(k = inl; k <= inr; k++){
		if(pre[prel] = in[k])
			break;
	}
	root->lchild = create_pre_in(prel+1, prel+numl, inl, k-1);
	root->rchild = create_pre_in(pre+numl+1, prer, k+1, inr);
	return root;
}
*/
void preorder(node *root1){
	if(root1 == NULL){
		return ;
	}
	printf("%d ", root1->data);
	preorder(root1->lchild);
	preorder(root1->rchild);
}
void inorder(node *root2){
	if(root2 == NULL)
		return ;
	inorder(root2->lchild);
	printf("%d ", root2->data);
	inorder(root2->rchild);
}
void postorder(node *root3){
	if(root3 == NULL)
		return ;
	postorder(root3->lchild);
	postorder(root3->rchild);
	printf("%d ", root3->data);
}

void layerorder(node* root){
	int num = 0;
	queue<node*> q;
	q.push(root);
	while(!q.empty()){
		node* now = q.front();
		q.pop();
		printf("%d", now->data);
		if(++num < n) printf(" ");
		if(now->lchild != NULL) q.push(now->lchild);
		if(now->rchild != NULL) q.push(now->rchild);
	}
}


int main(){
//	freopen("C:\\1.txt", "r", stdin);
	cin >> n;
	for(int i = 0; i < n; i++)
		scanf("%d", &post[i]);
	for(int i = 0; i < n; i++)
		scanf("%d", &in[i]);
//	preorder(create_post_in(0, n-1, 0, n-1));
//	cout << endl;
	layerorder(create_post_in(0, n-1, 0, n-1));
//	preorder(create_pre_in(0, n-1, 0, n-1));
	return 0;
} # include <iostream>
# include <queue>
using namespace std;
const int maxn = 1e5;

int n;
int pre[maxn], in[maxn], post[maxn];
struct node{
	int data; 
	node *lchild;
	node *rchild;
};

node* create_post_in(int postl, int postr, int inl, int inr){
	if(postl > postr)
		return NULL; 
	int k, numl;
	node *root = new node;
	root->data = post[postr];
	for(k = inl; k <= inr; k++){
		if(post[postr] == in[k])
			break;
	}
	numl = k - inl;
	root->lchild = create_post_in(postl, postl+numl-1, inl, k- 1);
	root->rchild = create_post_in(postl+numl, postr-1, k+1, inr);
	return root;
}
/*
node* create_pre_in(int prel, int prer, int inl, int inr){
	if(prel > prer) return NULL;
	int numl, k;
	node *root = new node;
	root->data = pre[prel];
	for(k = inl; k <= inr; k++){
		if(pre[prel] = in[k])
			break;
	}
	root->lchild = create_pre_in(prel+1, prel+numl, inl, k-1);
	root->rchild = create_pre_in(pre+numl+1, prer, k+1, inr);
	return root;
}
*/
void preorder(node *root1){
	if(root1 == NULL){
		return ;
	}
	printf("%d ", root1->data);
	preorder(root1->lchild);
	preorder(root1->rchild);
}
void inorder(node *root2){
	if(root2 == NULL)
		return ;
	inorder(root2->lchild);
	printf("%d ", root2->data);
	inorder(root2->rchild);
}
void postorder(node *root3){
	if(root3 == NULL)
		return ;
	postorder(root3->lchild);
	postorder(root3->rchild);
	printf("%d ", root3->data);
}

void layerorder(node* root){
	int num = 0;
	queue<node*> q;
	q.push(root);
	while(!q.empty()){
		node* now = q.front();
		q.pop();
		printf("%d", now->data);
		if(++num < n) printf(" ");
		if(now->lchild != NULL) q.push(now->lchild);
		if(now->rchild != NULL) q.push(now->rchild);
	}
}


int main(){
//	freopen("C:\\1.txt", "r", stdin);
	cin >> n;
	for(int i = 0; i < n; i++)
		scanf("%d", &post[i]);
	for(int i = 0; i < n; i++)
		scanf("%d", &in[i]);
//	preorder(create_post_in(0, n-1, 0, n-1));
//	cout << endl;
	layerorder(create_post_in(0, n-1, 0, n-1));
//	preorder(create_pre_in(0, n-1, 0, n-1));
	return 0;
}