docs: update SOLUTION_TREE.md

Author: yanglbme

Diff for: README.md

@@ -4,11 +4,11 @@
 
 <p align="center">
   <a href="https://github.com/doocs/leetcode"><img src="https://badgen.net/badge/lang/Java,CPP,Python,JS,Ruby,Go,.../orange?list=1" alt="language"></a>
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@@ -22,14 +22,14 @@ See [SOLUTION_TREE](/SOLUTION_TREE.md).
 
 ## Contributions
 I'm looking for long-term contributors/partners to this repo! Send me [PRs](https://github.com/doocs/leetcode/pulls) if you're interested! See the following:
-- Fork this repository to your own GitHub account and then [clone](https://help.github.com/articles/cloning-a-repository/) it to your local device.
-- Add or update file of the repository, then commit and push it to your GitHub repository.
+- `Fork` [this repository](https://github.com/doocs/leetcode) to your own GitHub account and then [`clone`](https://help.github.com/articles/cloning-a-repository/) it to your local device.
+- Make some changes to your leetcode repository, then `add`, `commit` and `push` it to your remote GitHub repository.
 - Submit a pull request with your changes!
-- For more details, see [CONTRIBUTING](/.github/CONTRIBUTING.md).
+- See [CONTRIBUTING](/.github/CONTRIBUTING.md) for more details.
 
 ![how-to-contribute](/img/how-to-contribute-yanglbme.png)
 
 ## Contributors
 This project exists thanks to all the people who contribute. 
 
-<a href="https://github.com/doocs/leetcode/graphs/contributors"><img src="https://opencollective.com/leetcode-280/contributors.svg?width=890&button=false" /></a>
+<a href="https://github.com/doocs/leetcode/graphs/contributors"><img src="https://opencollective.com/leetcode-280/contributors.svg?width=890&button=false" /></a>

Diff for: SOLUTION_TREE.md

@@ -581,8 +581,11 @@
 │   └── Solution.java
 ├── 0169.Majority Element
 │   └── Solution.java
+├── 0171.Excel Sheet Column Number
+│   └── Solution.java
 ├── 0172.Factorial Trailing Zeroes
-│   └── Solution.cpp
+│   ├── Solution.cpp
+│   └── Solution.java
 ├── 0175.Combine Two Tables
 │   └── README.md
 ├── 0176.Second Highest Salary