Houses on the street have sandbags outside permanently because of the continued risk of flooding
shading: “smooth gradients”
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* 核心思路：单调递增栈 + 控制删除位数（k0），优先移除高位大数，保证剩余数字最小
This is one of five facilities on the icy continent run by the British Antarctic Survey (BAS), the UK's polar research institute.