PAT (Advanced Level) 1110. Complete Binary Tree (25)

#include<cstdio>
#include<cstring>
#include<cmath>
#include<vector>
#include<map>
#include<queue>
#include<stack>
#include<algorithm>
using namespace std;

int n,root;
const int maxn=30;
struct Node
{
    int left;
    int right;
    int dep;
} s[maxn];
int flag[maxn];
vector<int>g[maxn];
int Max_dep=0;

void dfs(int x,int dep)
{
    Max_dep=max(dep,Max_dep);
    s[x].dep=dep;
    g[dep].push_back(x);

    if(s[x].left!=-1) dfs(s[x].left,dep+1);
    if(s[x].right!=-1) dfs(s[x].right,dep+1);
}

int main()
{
    memset(flag,0,sizeof flag);
    scanf("%d",&n);
    for(int i=0; i<n; i++)
    {
        char L[5],R[5];
        scanf("%s%s",L,R);
        if(L[0]==‘-‘) s[i].left=-1;
        else
        {
            int num=0;
            for(int k=0; L[k]; k++) num=num*10+L[k]-‘0‘;
            s[i].left=num;
            flag[num]=1;
        }

        if(R[0]==‘-‘) s[i].right=-1;
        else
        {
            int num=0;
            for(int k=0; R[k]; k++) num=num*10+R[k]-‘0‘;
            s[i].right=num;
            flag[num]=1;
        }
    }

    for(int i=0; i<n; i++)
        if(flag[i]==0) root=i;

    dfs(root,0);

    if(Max_dep==0)
    {
        printf("YES %d\n",g[Max_dep][g[Max_dep].size()-1]);
    }
    else
    {
        bool fail=0;
        for(int i=0; i<=Max_dep; i++)
        {
            if(i<Max_dep)
            {
                if(g[i].size()==(int)pow(2.0,i)) {}
                else fail=1;
            }
            else
            {
                for(int j=0; j<g[i].size(); j=j+2)
                {
                    if(j+1<g[i].size()&&j<g[i].size())
                    {
                        if(s[g[i-1][j/2]].left==g[i][j]&&s[g[i-1][j/2]].right==g[i][j+1]) {}
                        else fail=1;
                    }
                    else
                    {
                        if(s[g[i-1][j/2]].left==g[i][j]) {}
                        else fail=1;
                    }
                }
            }
        }

        if(fail==1) printf("NO %d\n",root);
        else printf("YES %d\n",g[Max_dep][g[Max_dep].size()-1]);
    }
    return 0;
}