PAT 1020. Tree Traversals (25)

题意：给出后序和中序遍历，求水平序列。

思路：

用递归做，注意root要事先建立。还有就是递归处的边界选择。

#include<cstdio>
#include<algorithm>
#include<cstring>
#include<iostream>
#include<stack>
#include<vector>
#include<queue>
#include<string>
#include<map>
using namespace std;
#define INF 99999999
#define M 300
struct node
{
int data;
struct node *lchild,*rchild;
};
int posto[M],mido[M];

struct node* buildtree(int ml,int mr,int pl,int pr)
{
int i=0;
if(ml>mr || pl >pr)
return NULL;
int proot=posto[pr];
for(i=ml;i<=mr;i++)
if(mido[i]==proot)
{
break;
}

struct node *Node;
Node = (struct node*)malloc(sizeof(struct node));
Node->data=proot;
Node->rchild = buildtree(i+1,mr,pr-1-(mr-i-1),pr-1);
Node->lchild = buildtree(ml,i-1,pl,pl+(i-1-ml));
return Node;
}

void levelprint(struct node *root)
{
struct node *Node;
vector<int> ans;
queue<struct node*> q;
q.push(root);
while(!q.empty())
{
Node = q.front();
q.pop();
ans.push_back(Node->data);
if(Node->lchild != NULL)
q.push(Node->lchild);
if(Node->rchild !=NULL)
q.push(Node->rchild);
}
int i;
for(i=0;i<ans.size();i++)
{
printf("%d",ans[i]);
if(i!=ans.size()-1)
printf(" ");
else printf("\n");
}
}

//start 21:54
//end 22:25
int main(){
int i,n;
struct node *root;
cin>>n;
for(i=0;i<n;i++)
scanf("%d",&posto[i]);
for(i=0;i<n;i++)
scanf("%d",&mido[i]);
root = (struct node*)malloc(sizeof(struct node));
root = buildtree(0,n-1,0,n-1);
levelprint(root);
return 0;
}