# 类别归档：LeetCode

LeetCode OJ is a platform for preparing technical coding interviews.

## 题目描述：

Given a binary tree, return the inorder traversal of its nodes' values.

```For example:
Given binary tree {1,#,2,3},
1
\
2
/
3
return [1,3,2].```

Note: Recursive solution is trivial, could you do it iteratively?

## 题目描述：

Write a SQL query to find all duplicate emails in a table named Person.

```+----+---------+
| Id | Email   |
+----+---------+
| 1  | a@b.com |
| 2  | c@d.com |
| 3  | a@b.com |
+----+---------+
For example, your query should return the following for the above ...```

## 题目描述：

The Employee table holds all employees including their managers. Every employee has an Id, and there is also a column for the manager Id.

```+----+-------+--------+-----------+
| Id | Name  | Salary | ManagerId |
+----+-------+--------+-----------+
| 1  | Joe   | 70000  | 3         |
| 2  | Henry | 80000  | 4         |
| 3  | Sam   | 60000 ...```

## 题目描述：

Write a SQL query to find all numbers that appear at least three times consecutively.

```+----+-----+
| Id | Num |
+----+-----+
| 1  |  1  |
| 2  |  1  |
| 3  |  1  |
| 4  |  2  |
| 5  |  1  |
| 6  |  2  |
| 7  |  2  |
+----+-----+
```

For example, given the above Logs table, 1 ...

## 题目描述：

Write a SQL query to rank scores. If there is a tie between two scores, both should have the same ranking. Note that after a tie, the next ranking number should be the next consecutive integer value. In other ...