1110 Complete Binary Tree （25 分）

1110 Complete Binary Tree （25 分）

Given a tree, you are supposed to tell if it is a complete binary tree.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤20) which is the total number of nodes in the tree -- and hence the nodes are numbered from 0 to N−1. Then N lines follow, each corresponds to a node, and gives the indices of the left and right children of the node. If the child does not exist, a - will be put at the position. Any pair of children are separated by a space.

Output Specification:

For each case, print in one line YES and the index of the last node if the tree is a complete binary tree, or NO and the index of the root if not. There must be exactly one space separating the word and the number.

Sample Input 1:

9
7 8
- -
- -
- -
0 1
2 3
4 5
- -
- -

Sample Output 1:

YES 8

Sample Input 2:

8
- -
4 5
0 6
- -
2 3
- 7
- -
- -

Sample Output 2:

NO 1

判断是否为完全树，如果是的话，请输出yes和最后一个节点的值，如果不是，输出no和根植，用了两种方法，均可ac，一种是dfs，一种是层次遍历

#include<iostream>
#include<string>
#include<vector> 
#include<cstdio>
#include<queue>
using namespace std;
struct node{
	int lchild,rchild;
};
struct node a[25];
int f1=0,f2=0;
int cnt;
void level(int root){
	queue<int> q;
	q.push(root);
	while(!q.empty()){
		cnt = q.front();
		q.pop();
		if(a[cnt].lchild!=-1){
			if(f1==1) f2 = 1;
			q.push(a[cnt].lchild);
		}else{
			f1 = 1;
		}
		if(a[cnt].rchild!=-1){
			if(f1==1) f2 =1;
			q.push(a[cnt].rchild);
		}else{
			f1 = 1;
		}
		
	}
}
int main(){
	int n;
	vector<int> book(25,0);
	cin >> n;
	for(int i = 0;i < n;i++){
		string l,r;
		cin >> l >> r;
		if(l=="-"){
			a[i].lchild = -1;
		}else{
			a[i].lchild = stoi(l);
			book[stoi(l)] = 1;
		}
		if(r=="-"){
			a[i].rchild = -1;
		}else{
			a[i].rchild = stoi(r);
			book[stoi(r)] = 1;
		}
	} 
	int root=0;
	while(book[root] != 0){
		root++;
	}
	level(root);
	if(f2==0){
		cout << "YES" << " " << cnt << endl; 
	}else{
		cout << "NO" << " " << root << endl;
	}
}

#include<iostream>
#include<string>
#include<vector> 
#include<cstdio>
#include<queue>
using namespace std;
struct node{
	int lchild,rchild;
};
struct node a[500];
int ans = -1;
int r;
void dfs(int root,int cnt){
	if(cnt > ans){
		ans = cnt;
		r = root;	
	}
	if(a[root].lchild != -1){
		dfs(a[root].lchild,cnt*2);
	}
	if(a[root].rchild != -1){
		dfs(a[root].rchild,cnt*2+1);
	}
}
int main(){
	int n;
	vector<int> book(500,0);
	cin >> n;
	for(int i = 0;i < n;i++){
		string l,r;
		cin >> l >> r;
		if(l=="-"){
			a[i].lchild = -1;
		}else{
			a[i].lchild = stoi(l);
			book[stoi(l)] = 1;
		}
		if(r=="-"){
			a[i].rchild = -1;
		}else{
			a[i].rchild = stoi(r);
			book[stoi(r)] = 1;
		}
	} 
	int root=0;
	while(book[root] != 0){
		root++;
	}
	dfs(root,1);
	if(ans==n){
		cout << "YES" << " " << r << endl; 
	}else{
		cout << "NO" << " " << root << endl;
	}
}