二叉树的操作总结

最近做PAT总是涉及二叉树的操作问题，现在来总结一下。。

已知前序中序，求后序和层次遍历

#include<stdio.h>
#include<stdlib.h>
#include<queue>
using namespace std;

typedef struct tree{
	struct tree *l,*r;
	int data;
}tree;

int pre[105],in[105];

tree* build(int *a,int *b,int c){
	tree *t;
	for(int i = 0;i<c;i++){
		if(a[0] == b[i]){
			t = (tree*) malloc(sizeof(tree));
			t->data = a[0];
			t->l = build(a+1,b,i);
			t->r = build(a+i+1,b+i+1,c-i-1);
			
			return t;
		}
	}
	return NULL;
}

void postorder(tree* a){                //递归后序输出 
	if(a != NULL){
		postorder(a->l);
		postorder(a->r);
		if(a->data == pre[0])
			printf("%d\n",a->data);
		else printf("%d ",a->data);
	}
}

void leveltravel(tree *a){             //非递归层次遍历 
	queue<tree*> q;
	tree* p = NULL;
	if(a)
		q.push(a);
	while(!q.empty()){
		p = q.front();
		q.pop();
		printf("%d ",p->data);
		if(p->l)
			q.push(p->l);
		if(p->r)
			q.push(p->r);
	}
}

int main(){
	int n;
	tree* root;
	while(~scanf("%d",&n)){
		printf("输入前序：");
		for(int i = 0;i<n;i++)
			scanf("%d",pre+i);
		printf("输入中序：");
		for(int i = 0;i<n;i++)
			scanf("%d",in+i);
		root = build(pre,in,n);
		tree* s = root;
		printf("输出后序遍历：");
		postorder(s);
		printf("输出层次遍历：");
		leveltravel(s);
	}
	return 0;
}

已知后序中序，求前序和层次遍历

#include<stdio.h>
#include<stdlib.h>
#include<queue>
using namespace std;

typedef struct tree{
	struct tree *l,*r;
	int data;
}tree;

int n,post[105],in[105],count;
tree* root;

tree* build(int *a,int *b,int c){
	tree* t;
	for(int i = 0;i<c;i++){
		if(a[c-1] == b[i]){
			t = (tree*) malloc(sizeof(tree));
			t->data = a[c-1];
			t->l = build(a,b,i);
			t->r = build(a+i,b+i+1,c-i-1);
			
			return t;
		}
	}
	return NULL;
}

void preorder(tree *a){
	if(a != NULL){
		if(a->data == in[n-1])
			printf("%d\n",a->data);
		else printf("%d ",a->data);
		preorder(a->l);
		preorder(a->r);
	}
}

void leveltravel(tree *a){
	queue<tree*> q;
	tree *p = NULL;
	if(a)
		q.push(a);
	while(!q.empty()){
		p = q.front();
		q.pop();
		printf("%d ",p->data);
		if(p->l)
			q.push(p->l);
		if(p->r)
			q.push(p->r);
	}
}

int atLevel(tree *a,int x){
	if(!a || x < 0)
		return 0;
	if(x == 0){
		count++;
		if(count == n)
			printf("%d\n",a->data);
		else  printf("%d ",a->data);
		return 1;
	}
	return atLevel(a->l,x-1)+atLevel(a->r,x-1);
}

void leveltravel2(tree *a){					//递归层次遍历 
	for(int i = 0; ;i++){
		if(!atLevel(a,i))
			break;
	}
}

int main(){
	while(~scanf("%d",&n)){
		count = 0;
		printf("输入后序：");
		for(int i = 0;i<n;i++)
			scanf("%d",post+i);
		printf("输入中序：");
		for(int i = 0;i<n;i++)
			scanf("%d",in+i);
		root = build(post,in,n);
		tree *s = root;
		printf("输出前序遍历：");
		preorder(s);
		printf("输出非递归层次遍历：");
		leveltravel(s);
		printf("\n");
		printf("输出递归层次遍历：");
		leveltravel2(s);
	}
}