A1110 Complete Binary Tree [完全二叉树判定]

思路：利用层序遍历判断是否是一棵完全二叉树，给的下标同样利用二叉树的静态写法

#include<iostream>
#include<vector>
#include<queue>
#include<stack>
#include<string>
using namespace std;
const int maxn = 21;
int n, last;
struct node
{
	int lchild, rchild;
}Node[maxn];
bool notroot[maxn];
int input(string s)
{
	if (s[0] == '-')
		return -1;
	else
	{
		if (s.size() == 1)
		{
			notroot[s[0] - '0'] = true;
			return s[0] - '0';
		}
		else
		{
			notroot[(s[0] - '0') * 10 + (s[1] - '0')] = true;
			return (s[0] - '0') * 10 + (s[1] - '0');
		}				
	}
}
int findroot()
{
	for (int i = 0; i < n; i++)
	{
		if (notroot[i] == false)
			return i;
	}
}
bool bfs(int root)
{
	queue<int>q;
	q.push(root);
	while (n)
	{
		int temp = q.front();
		q.pop();
		if (temp == -1)
			return false;
		n--;
		last = temp;
		q.push(Node[temp].lchild);
		q.push(Node[temp].rchild);
	}
	return true;
}
int main()
{
	cin >> n;	
	for (int i = 0; i < n; i++)
	{
		string s1, s2;
		cin >> s1 >> s2;
		Node[i].lchild = input(s1);
		Node[i].rchild = input(s2);
	}
	int root = findroot();
	int a = bfs(root);
	if (a)
	{
		cout << "YES " << last << endl;
	}
	else
	{
		cout << "NO " << root << endl;
	}
}