hdu 1710 binary tree traversals 二叉树遍历

根据二叉树的前序遍历和中序遍历求后序遍历的题。

一开始的方法是根据前序遍历和中序遍历构建二叉树，再从二叉树开始后序遍历。事实证明我还是too young too naive，一开始还好好的，后来这递归被我越写越糟糕，都看不下去了，好不容易程序运行起来了，对了下答案也没问题，就交了上去，结果返回了RE……………………

好难过啊QAQ

于是去搜题解，发现有人说用结构构建树用了太多空间导致RE，但我觉得不应该啊QAQ，然后又找到个人也是构建了树再遍历的，不过他用的是指针，我直接开的两个整型来保存。（喵的现在这天气居然有人进来还开空调（╯‵□′）╯ノ┻━┻☆）可能就是这两个整型导致RE了？

总之先贴上错误的代码……

#include<cstdio>
#include<iostream>
#define MAXN 2005
#define Lc (id<<1)
#define Rc (Lc|1)
using namespace std;
int preorder[MAXN], inorder[MAXN], postorder[MAXN];
int tree[MAXN*4];
bool haveval[MAXN*4];
int orderpoint;
int search(int sx, int ex, int target){
for(int i=sx;i<=ex;i++){
if(inorder[i]==target)return i;
}
}
int id;
void buildtree(int left, int mid, int right, int id){
if(left==right){
return ;
}
bool inleft=false;
int leftu, rightu;
tree[id]=inorder[mid];
haveval[id]=true;
if(left<=mid-1){
orderpoint++;
leftu=search(left, mid-1, preorder[orderpoint]);
}
else leftu=left;
if(left<=mid-1)
buildtree(left, leftu, mid-1, Lc);
if(mid!=leftu){
tree[Lc]=inorder[leftu];
haveval[Lc]=true;
inleft=true;
}
if(mid+1<=right){
orderpoint++;
rightu=search(mid+1, right, preorder[orderpoint]);
}
else rightu=right;
if(mid+1<=right)
buildtree(mid+1, rightu, right, Rc);
if(mid!=rightu){
if(!inleft){
tree[Lc]=inorder[rightu];haveval[Lc]=true;
}
else {
tree[Rc]=inorder[rightu];haveval[Rc]=true;
}
}
}
void postsearch(int id){
if(!haveval[id])return ;
postorder[++orderpoint]=tree[id];
postsearch(Rc);
postsearch(Lc);
}
int main(){
int n;
while(cin>>n){
memset(haveval, false, sizeof(haveval));
for(int i=0;i<n;i++)
scanf("%d", &preorder[i]);
for(int i=0;i<n;i++){
scanf("%d", &inorder[i]);
if(inorder[i]==preorder[0])id=i;
}
orderpoint=0;
buildtree(0, search(0, n-1, preorder[0]), n-1, 1);
orderpoint=0;
postsearch(1);
for(int i=n;i>=2;i--)printf("%d ", postorder[i]);
cout<<postorder[1]<<endl;
}
return 0;
}

总而言之暂时没想到哪里错了Orz……本渣还是研究下题解重写吧Orz……

*******************重写完毕************************

来个AC的代码

#include<cstdio>
#include<iostream>
using namespace std;
#define MAXN 1005
int preorder[MAXN], inorder[MAXN], postorder[MAXN];
int prept, postpt;
void search(int left, int right){
if(left>right)return ;
if(left==right){
postorder[postpt++]=inorder[left];
prept++;
return ;
}
int inpt;
for(inpt=left;inorder[inpt]!=preorder[prept];inpt++);
prept++;
search(left, inpt-1);
search(inpt+1, right);
postorder[postpt++]=inorder[inpt];
}
int main(){
int n;
while(cin>>n){
for(int i=1;i<=n;i++)scanf("%d", &preorder[i]);
for(int i=1;i<=n;i++)scanf("%d", &inorder[i]);
prept=1;postpt=1;
search(1, n);
for(int i=1;i<n;i++)printf("%d ", postorder[i]);
cout<<postorder
<<endl;
}
return 0;
}