过去，国内生产这些线材都是用来出口的，但在 2009 年开始国内的需求开始暴涨。
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For example, a 500km route might be broken down into ~100 such shortcuts. If each A* shortcut calculation explores 100-1000 detailed road segments, the total detailed segments visited by A* might be around 10,000-50,000. Compare this to the 1,000,000+ segments the old A* might have needed for the entire route!
stack2.pop(); // 弹出无效的候选值