PAT 甲级 1110 Complete Binary Tree

https://pintia.cn/problem-sets/994805342720868352/problems/994805359372255232

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

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

代码：

#include <bits/stdc++.h>
using namespace std;

int N;
int vis[110];
int ans = -1, temp;

struct Node{
    int l;
    int r;
}node[110];

int StringtoInt(string s) {
    int len = s.length();
    int sum = 0;
    for(int i = 0; i < len; i ++) {
        sum = sum * 10 + (s[i] - '0');
    }
    return sum;
}

void dfs(int st, int step) {
    if(step > ans) {
        ans = step;
        temp = st;
    }

    if(node[st].l != -1) dfs(node[st].l, step * 2);
    if(node[st].r != -1) dfs(node[st].r, step * 2 + 1);
}

int main() {
    scanf("%d", &N);
    memset(vis, 0, sizeof(vis));
    for(int i = 0; i < N; i ++) {
        string s1, s2;
        cin >> s1 >> s2;
        if(s1 == "-") {
            node[i].l = -1;
        } else if(s1 != "-"){
            node[i].l = StringtoInt(s1);
            //cout << node[i].l << endl;
            vis[node[i].l] = 1;
        }

        if(s2 == "-") {
            node[i].r = -1;
        } else if(s2 != "-") {
            node[i].r = StringtoInt(s2);
            vis[node[i].r] = 1;
            //cout << node[i].r << endl;
        }
    }

    int root = 0;
    while(vis[root]) root ++;
    dfs(root, 1);

    if(ans == N)
        printf("YES %d
", temp);
    else printf("NO %d
", root);
    return 0;
}

　　判断是不是完全二叉树要判断这个树是不是满的看是不是最大的节点数等于一共的节点数目 dfs 求最大的节点下标