题目地址

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

  • -
  • -
  • -
  1. 1

2 3
4 5

  • -

  • -

    Sample Output 1:

YES 8

Sample Input 2:
8

  • -
  1. 5

0 6

  • -
  1. 3
  • 7
  • -

  • -

    Sample Output 2:

NO 1

#include <iostream>
#include <vector>
#include<algorithm>
#include <cmath>
#include<map>
#include<cstring>
#include<queue>
#include<string>
#include<set>
#include<stack>
using namespace std;
typedef long long ll;
const int maxn=100010,inf=100000000;
int n,root,ans=-1;
struct node{
    int data,lchild,rchild;
}s[maxn];
int last_node,max_index=-1;            //有静态数组树思想；
void travel(int root,int index){        //变动树，判断idx；
    if(index>max_index&&root!=-1){
        last_node=root;
        max_index=index;
    }
    if(s[root].lchild!=-1) travel(s[root].lchild,index*2);
    if(s[root].rchild!=-1) travel(s[root].rchild,index*2+1);
}
int main() {
    cin>>n;string v1,v2;bool not_root[maxn]={0};
    for(int i=0;i<n;i++){
        cin>>v1>>v2;
        if(v1=="-") s[i].lchild=-1;
        else {
            s[i].lchild=stoi(v1);not_root[stoi(v1)]=1;
            }
        if(v2=="-") s[i].rchild=-1;
        else {
            s[i].rchild=stoi(v2);not_root[stoi(v2)]=1;
            }
    }
    for(int i=0;i<n;i++){
        if(!not_root[i]) root=i;
    }
    travel(root,1);
    if(max_index==n) cout<<"YES "<<last_node;
    else cout<<"NO "<<root;
}