PAT-A-1086 报告Bug about pat HOT 4 CLOSED

#include <cstdio>
#include <vector>
#include <stack>
#include <cstring>
using namespace std;
vector<int> pre, in, post,value;
void postorder(int root, int start, int end) {
	if (start > end) return;
	int i = start;
	while (i < end && in[i] != pre[root]) i++;
	postorder(root + 1, start, i - 1);
	postorder(root + 1 + i - start, i + 1, end);
	post.push_back(pre[root]);
}
int main() {
	int n;
	scanf("%d", &n);
	char str[5];
	stack<int> s;
	int key=0;
	while (~scanf("%s", str)) {
		if (strlen(str) == 4) {
			int num;
			scanf("%d", &num);
			value.push_back(num);
			pre.push_back(key);
			s.push(key++);
		}
		else {
			in.push_back(s.top());
			s.pop();
		}
	}
	postorder(0, 0, n - 1);
	printf("%d", value[post[0]]);
	for (int i = 1; i < n; i++)
		printf(" %d",value[post[i]]);
	return 0;
}

//之前设置bool flag=false;

	if (flag)
		cout << ' ';
	cout << value[pre[root]];
	flag = true;