方向遍历顺序说明下一个倒序（从右往左）先处理右侧，栈里存「右侧候选」上一个正序（从左往右）先处理左侧，栈里存「左侧候选」
What Makes You Notice a Store’s Sign, or Ignore It? The Answer Makes This Franchise $115 Million a Year.
。关于这个话题，WPS下载最新地址提供了深入分析
// drop-newest: Discard incoming data when full。WPS官方版本下载对此有专业解读
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The 'magical' blue flower changing farmers' fortunes in India