1110 complete binary tree (25 points)

The main idea of the topic : Given the left and right children of each node , Judge whether this tree is a complete binary tree

If the maximum node number is equal to the number of nodes, then it is a complete binary tree

#include <iostream>
#include <queue>
#include <unordered_map>
using namespace std;
int n,last,res;
struct Eg
{
	string l,r;
}e[100];
unordered_map<int,int>mp;
void dfs(int u,int idx)
{   
    if(idx > last) 
    {
        last = idx;
        res = u;
    }
	if(e[u].l != "-") dfs(stoi(e[u].l),idx << 1);
	if(e[u].r != "-") dfs(stoi(e[u].r),idx << 1 | 1);
}
int main()
{	
	cin >> n;
	for(int i = 0; i < n; i ++)
	{
		string a,b;
		cin >> a >> b;
		if(a != "-") mp[stoi(a)] = 1;
		if(b != "-") mp[stoi(b)] = 1;
		e[i] = {a,b};
	}
	int u;
	for(int i = 0; i < n; i ++) if(!mp[i]) u = i;// root 
	dfs(u,1);
	if(last == n) cout << "YES" << ' ' << res << endl;
	else cout << "NO" << ' ' << u << endl;
	return 0;
}