1020 Tree Traversals (25)

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
根据后序和中序建树，层序输出。

#include<cstdio> 
#include<cstring>
#include<queue>
#include<algorithm>
using namespace std;
const int maxn=100;
struct node{
    int data;
    node *lchild,*rchild;
};
int n,pre[maxn],in[maxn],post[maxn];

node *creat(int postl,int postr,int inl,int inr){
    if(postl>postr) return NULL;
    node *root=new node;
    root->data =post[postr];
    int k;
    for(k=inl;k<=inr;k++){
        if(in[k]==post[postr])
            break;
    }
    int numleft=k-inl;
    root->lchild =creat(postl,postl+numleft-1,inl,k-1);
    root->rchild =creat(postl+numleft,postr-1,k+1,inr);
    return root;
}
int num=0;
void bfs(node *root){
    queue<node*>q;
    q.push(root) ;
    while(!q.empty() ){
        node *now=q.front() ;
        q.pop() ;
        printf("%d",now->data );
        num++;
        if(num<n) 
            printf(" ");
        if(now->lchild !=NULL) q.push(now->lchild ) ;
        if(now->rchild !=NULL) q.push(now->rchild ) ;
    }
}
int main(){
    scanf("%d",&n);
    for(int i=0;i<n;i++){
        scanf("%d",&post[i]);
    }
    for(int i=0;i<n;i++){
        scanf("%d",&in[i]);
    }
    node *root=creat(0,n-1,0,n-1);
    bfs(root);
    return 0;
}