第四十九条 纳税人适用退（免）税的出口业务，可以放弃退（免）税，选择免征增值税或者缴纳增值税，自放弃退（免）税之日次月起，适用退（免）税的出口业务免征增值税或者按规定缴纳增值税。
Овечкин продлил безголевую серию в составе Вашингтона09:40
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The U.S. women also beat Canada 2-1 in overtime, the first time the Americans swept both Olympic hockey tournaments. The celebration of the twin victories has been shadowed by U.S. politics almost since the final horn of the men’s game.
* 核心思路：链表转数组 + 单调栈（从后往前遍历），时间复杂度O(n)，空间复杂度O(n)