1086 tree traversals again (25 points)

Stacking is the preamble , Out of the stack is the middle order  

#include <iostream>
#include <vector>
using namespace std;
const int N = 50;
int stk[N],top,f;
vector<int>pre,in;
// Stacking is the preamble , Out of the stack is the middle order  
void dfs(int preL,int preR,int inL,int inR)
{   
	if(preL > preR) return ;
	int k = inL;
	while(in[k] != pre[preL]) k ++;
	dfs(preL + 1,preL + k - inL,inL,k - 1);
	dfs(preL + 1 + k - inL,preR,k + 1,inR);
	if(f != 0) cout << ' ';
	cout << pre[preL];f = 1;
}
int main()
{
	int n,x,cnt = 0;
	string s;
	cin >> n;
	while(cnt != n)
	{
		cin >> s;
		if(s[1] == 'u')
		{
			cin >> x;
			stk[ ++ top] = x;
			pre.push_back(x);
		}
		else in.push_back(stk[top --]),cnt ++;
	}
	dfs(0,n - 1,0,n - 1);
	return 0;
 }