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21. 一个人站在坐标(0,0)处,面朝 x 轴正方向。第一轮,他向前走 1 单位距离,然后右转;第二轮,他向前走 2 单位距离,然后右转;第三轮,
他向前走 3 单位距离,然后右转……他一直这么走下去。请问第 2017轮后,他的坐标是:(___ , ___)。
坐标为 ,
22如下图所示,共有 13个格子。对任何一个格子进行一次操作,会使得它自己以及与它上下左右相邻的格子中的数字改变(由 1 变 0,或由 0 变 1)。
现在要使得所有的格子中的数字都变为 0,至少需要_____次操作。