题目： https://pintia.cn/problem-sets/1268384564738605056/problems/1274008636207132673

Given a tree, you are supposed to list all the leaves in the order of top down, and left to right.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N (≤10) 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 test case, print in one line all the leaves' indices in the order of top down, and left to right. There must be exactly one space between any adjacent numbers, and no extra space at the end of the line.

Sample Input:

8
1 -
- -
0 -
2 7
- -
- -
5 -
4 6

 

Sample Output:

4 1 5

题解： https://cloud.tencent.com/developer/article/1390933
代码：

#include <cstdio>
#include <iostream>
#include <cstring>
using namespace std;

struct Tree
{
    char rchild, lchild;
    void clear()
    {
        rchild = 0;
        lchild = 0;
    }
};

Tree head[15];
int q[15];  //模拟队列 

int findRoot(Tree head[], int n)
{
    int isRoot[15];  //相当于布尔数组 
    char left, right;
    memset(isRoot, 0, sizeof(isRoot));
    for(int i = 0; i < n; i++)
    {
        left = head[i].lchild - '0';
        if(left >= 0)
            isRoot[left] = 1;
        right = head[i].rchild - '0';
        if(right >= 0)
            isRoot[right] = 1;
    }
    for(int i = 0; i < n; i++)
    {
        if(isRoot[i] == 0)
            return i;
    }
}

void bfs(Tree head[], int n, int root)
{
    int first = 1;//判断是不是第一个输出 
    int rear = 0, front = 0;//队列首尾 
    q[rear++] = root;
    while(front != rear)//当队列不为空 
    {
        if(head[q[front]].lchild != '-')
        {
            q[rear] = head[q[front]].lchild - '0';
            rear++;
        }
        if(head[q[front]].rchild != '-')
        {
            q[rear] = head[q[front]].rchild - '0';
            rear++;
        }
        if(head[q[front]].lchild == '-' && head[q[front]].rchild == '-')
        {
            if(first) 
            {
                cout << q[front];
                first = 0;
            }
            else
                cout << " " << q[front];
        } 
        front++;
    }
}

int main()
{
//    freopen("listLeaves.txt", "r", stdin);
    int n;
    int root;
    char c, d;
    while(scanf("%d", &n) != EOF)
    {
        for(int i = 0; i < n; i++)
            head[i].clear();
        memset(q, 0, sizeof(q));
        for(int i = 0; i < n; i++)
        {
            cin >> head[i].lchild >> head[i].rchild;
        }
        root = findRoot(head, n);
        bfs(head, n, root);
    }
    return 0;
}