foreground and background colors at work
习题链接：LeetCode 1944. 队列中可以看到的人数，推荐阅读服务器推荐获取更多信息
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// First, we acquire a reader that gives an exclusive lock
Number (6): Everything in this space must add up to 6. The answer is 6-3, placed vertically; 3-2, placed vertically.，详情可参考同城约会