数学·结合·排序 模式

识别信号

• Can the candidate handle edge cases like leading zeros and negative numbers effectively?
• Does the candidate demonstrate an understanding of sorting algorithms?
• Check if candidate handles repeated digits correctly.

解题流程

1. 1. 明确窗口/状态定义
2. 2. 更新状态并维护约束
3. 3. 用边界样例验证

常见失分点

• Forgetting to handle leading zeros for positive numbers.
• Forgetting that digits can repeat and pair with themselves.