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.

原题

判断一颗二叉树是不是完全的，只需要判断能否用大小为n的堆来表示这棵树。（树的大小为n）
用int nl[21]={-1},nr[21]={-1}来表示一棵二叉树。

#include <cstdio>
#include <string>
#include <vector>
#include <set>
#include <cmath>
#include <algorithm>
#include <fstream>
#include <iostream>
#include <limits>
#include <map>
#include <unordered_set>
#include <assert.h>
#include <memory.h>
using namespace std;

#define INF INT_MAX-10000
#define repeat(n) for(int _i=0;_i<n;_i++)
//    typedef long long ll;
int n;
#define INPUT cin>>n
int nl[21]={-1},nr[21]={-1},heep[21]={1},not_root[21]={0};

bool is_tree(int node,int no)
{
    if(node==-1)
        return true;
    if(no>n) return false;
    heep[no]=node;
    return is_tree(nl[node],2*no)&&is_tree(nr[node],2*no+1);
}
int main()
{
#ifdef _DEBUG
    fstream cin("input.txt");
#endif
    while(INPUT)
    {
        memset(nl,-1,21*4);
        memset(nr,-1,21*4);
        memset(heep,-1,21*4);
        int t=0;
        assert(n<21);
        while(t<n)
        {
            int a=0,b=0;string str;
            if(scanf("%d",&a))
                nl[t]=a,not_root[a]=1;
            if(scanf("%d",&b))
                nr[t]=b,not_root[b]=1;
            assert(a<n);assert(b<n);
            t++;
        }
        int p=0;
            while(not_root[p])
                p++;
        if(is_tree(p,1))
        {
            cout<<"YES "<<heep[n]<<endl;
        }else
        {
            
            cout<<"NO "<<p<<endl;
        }

    }
    return 0;
}