A1086 Tree Traversals Again [前序中序建树]

#include<iostream>
#include<vector>
#include<queue>
#include<stack>
#include<cstring>
using namespace std;
const int maxn = 31;
struct node
{
	int data;
	node* left;
	node* right;
};
int pre[maxn], in[maxn], post[maxn];
int n;
node* create(int prel, int prer, int inl, int inr)
{
	if (prel > prer)
		return NULL;
	node* root = new node;
	root->data = pre[prel];
	int i;
	for (i = inl; i <= inr; i++)
	{
		if (in[i] == pre[prel])
			break;
	}
	int numleft = i - inl;
	root->left = create(prel+1, prel + numleft , inl, i - 1);
	root->right = create(prel + numleft+1, prer, i + 1, inr);
	return root;
}
int num = 0;
void postorder(node* root)
{
	if (root == NULL)
		return;
	postorder(root->left);
	postorder(root->right);
	cout << root->data;
	num++;
	if (num < n)
		cout << " ";
}
int main()
{
	cin >> n;
	char str[5];
	stack<int>st;
	int x, preindex=0, inindex = 0;
	for (int i = 0; i < 2 * n; i++)
	{
		cin >> str;
		if (strcmp(str, "Push") == 0)
		{
			cin >> x;
			pre[preindex++] = x;
			st.push(x);
		}
		else
		{
			in[inindex++] = st.top();
			st.pop();
		}
	}
	node* root = create(0, n - 1, 0, n - 1);
	postorder(root);
	return 0;
}