Green: Board stuff
int getDigit(int num, int digit) {。关于这个话题，safew官方下载提供了深入分析
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"But then you start to get out, and you see whales, seals and islands on boats, and then little trips out in small aircraft. And you think, 'this is pretty brilliant'. This year, I've been so lucky to see an emperor penguin colony. It's like something from a David Attenborough documentary."。关于这个话题，Line官方版本下载提供了深入分析
# 过程中可能需要输入 y 来确认
int i = 0, j = 0, k = left; // i:左数组指针, j:右数组指针, k:原数组指针