PAT 1110 Complete Binary Tree

1110. Complete Binary Tree (25)

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

#include <cstdio>
#include <cstring>
#include <queue>
#include <iostream>
using namespace std;
int tree[25][2];
int n,fa;
void dfs(){
	int last=fa,count=1;
	queue<int> q;
	q.push(fa);
	while(!q.empty()){
		int t=q.front();
		q.pop();
		if(tree[t][0]!=-1){
			q.push(tree[t][0]);
			last=tree[t][0];
			count++;
		}
		else{
			break;
		}
		if(tree[t][1]!=-1){
			q.push(tree[t][1]);
			last=tree[t][1];
			count++;
		}
		else{
			break;
		}
	}
	if(count==n){
		cout<<"YES "<<last<<endl;
	}
	else{
		cout<<"NO "<<fa<<endl;
	}
}
int Get(){
	char s[5];
	scanf("%s",s);
	if(s[0]=='-'){
		return -1;
	}
	if(s[1]){
		return (s[0]-'0')*10+s[1]-'0';
	}
	else{
		return s[0]-'0';
	}
}
int main(){
	char ch[3];
	int book[25];
	memset(book,0,sizeof(book));
	cin>>n;
	for(int i=0;i<n;i++){
		tree[i][0]=Get();
		if(tree[i][0]!=-1)
			book[tree[i][0]]=1;
		tree[i][1]=Get();
		if(tree[i][1]!=-1)
			book[tree[i][1]]=1;
	}
	for(int i=0;i<n;i++){
		if(!book[i]){
			fa=i;
			break;
		}
	}
	dfs();
	return 0;
}