// 计算天数：栈非空→栈顶索引-当前索引；栈空→0（易错点3：索引差别写反）
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"It took me six months until I could feel happy again, just emotionally.，详情可参考爱思助手下载最新版本
For multiple readers，这一点在51吃瓜中也有详细论述