blog: fertility policy

[shenxiangzhuang]

Pull Request Description

[Provide a brief description of the changes in this pull request]

Related Issue

[If applicable, link to the related issue(s) this PR addresses]

Type of Change

• New problem and solution
• Problem or solution improvement
• Bug fix
• Documentation update
• Translation
• Other (please specify)

Checklist

• I have read the CONTRIBUTING document
• I have tested my changes locally
• My code follows the project's coding style
• I have updated the documentation accordingly
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have checked my code and corrected any misspellings

For New Problems

• The problem is provided in both English and Chinese
• The difficulty level is specified
• A solution approach or hint is included
• The problem file follows the correct naming convention and is placed in the appropriate directory

For Solution Updates

• The solution is mathematically correct
• The solution is clearly explained
• Code implementations (if any) are correct and efficient

Additional Notes

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