树的遍历存题

https://pintia.cn/problem-sets/994805342720868352/exam/problems/994805388447170560

https://pintia.cn/problem-sets/994805342720868352/exam/problems/994805376476626944

https://pintia.cn/problem-sets/994805342720868352/exam/problems/994805372601090048

https://pintia.cn/problem-sets/994805342720868352/exam/problems/994805362341822464

https://pintia.cn/problem-sets/994805342720868352/exam/problems/994805521431773184

https://pintia.cn/problem-sets/994805342720868352/exam/problems/994805424153280512