A1138 Postorder Traversal [前序中序建树]

#include<iostream>
#include<vector>
#include<map>
#include<string>
#include<cstring>
#include<cstdio>
#include<algorithm>
#include<set>
#include<queue>
#include<unordered_set>
using namespace std;
vector<int>pre, in;
struct node
{
	int data;
	node* left, * right;
};
node* buildtree(int prel, int prer, int inl, int inr)
{
	if (prel > prer)
		return NULL;
	node* root = new node;
	root->left = NULL;
	root->right = NULL;
	root->data = pre[prel];
	int i;
	for (i = inl; i <=inr; i++)
	{
		if (in[i] == pre[prel])
		{
			break;
		}
	}
	int leftnum = i - inl;
	root->left=buildtree(prel + 1, prel + leftnum, inl, i - 1);
	root->right = buildtree(prel + leftnum + 1, prer, i + 1, inr);
	return root;
}
node* findleft(node* root)
{
	if (root->left == NULL && root->right == NULL)
		return root;
	if (root->left!=NULL)
	{
		root = root->left;
	}
	else if(root->right!=NULL)
	{
		root = root->right;
	}
	findleft(root);
}
int main()
{
	int n,temp; cin >> n;
	for (int i = 0; i < n; i++)
	{
		cin >> temp;
		pre.push_back(temp);
	}
	for (int i = 0; i < n; i++)
	{
		cin >> temp;
		in.push_back(temp);
	}
	node* root = new node;
	root = buildtree(0, n - 1, 0, n - 1);
	node* left = new node;
	left = findleft(root);
	cout << left->data << endl;
}