“In China, labor costs are $2 to $3 an hour. In America they are $20 an hour.”
Hebrew Paseq: a non-obvious finding
，更多细节参见91视频
Dr. John Ackerman, an expert on youth suicide prevention who was not involved in Instagram's alert feature, told Mashable that it appeared to be carefully considered. Instagram said it relied on feedback from a group of experts it assembled on suicide and self-harm. (Instagram does not publicize the members of its advisory group.)
// 易错点2：遍历结束后k仍0 → 栈是递增的，末尾数字更大，移除末尾k位