一个进栈的所有出栈序列

void (stack<int> v) { 
	while (v.size() != 0) {
		cout<<v.top()<<" ";
		v.pop();
	}
	cout<<endl;
}
//a存放入栈序列，b模拟入栈， c存放可能的出栈的序列
void dfs(stack<int> a, stack<int> b, stack<int> c) {           
	
	if (a.size() == 0 && b.size() == 0 ) {
		print(c);	
		return;
	} 
	
	if (a.size() != 0) {		//入栈 
		int val = a.top();
		b.push(val);
		a.pop();
		dfs(a, b, c);
		b.pop();
		a.push(val);
	} 
	if (b.size() != 0) {		//出栈 
		int val = b.top();
		c.push(val);
		b.pop();
		dfs(a, b, c);
		c.pop();
		b.push(val);
	}
	
	return;
}