二叉树前序中序遍历求后序遍历

#include <iostream>
#include <cstdio>
#include <queue>
#include <cstring>
using namespace std;
const int MAXN = 100;
struct Node {
    int value;
    Node *left_child;
    Node *right_child;
    Node () {
        left_child = right_child = NULL;
    }
};
bool first = true;
void Pos_order(Node *tree) {
    if(tree->left_child != NULL) {
        Pos_order(tree->left_child);
    }
    if(tree->right_child != NULL) {
        Pos_order(tree->right_child);
    }
    if(first) {
        cout << tree->value;
        first = false;
    } else cout << " " << tree->value;
}

Node* build(int pre[], int in[], int n) {
    if(n == 0) return NULL;
    Node *tmp = new Node;
    for(int i = 0; i < n; i++) {
        if(in[i] == pre[0]) {
            tmp->value = pre[0];
            tmp->left_child = build(pre+1, in, i);
            tmp->right_child = build(pre+i+1, in+i+1, n-i-1);
            return tmp;
        }
    }
    return NULL;
}

int main() {
    int n, pre[MAXN], in[MAXN];
    scanf("%d", &n);
    first = false;
    for(int i = 0; i < n; i++) scanf("%d", &in[i]);
    for(int i = 0; i < n; i++) scanf("%d", &pre[i]);
    Node *tree = build(pre, in, n);
    Pos_order(tree);
    return 0;
}