Richard MorrisTechnology reporter
The US has been accused of “shameless exploitation” over a health financing agreement with Zambia worth more than $1bn (£740m), amid warnings that the country is getting a raw deal from the Trump administration.
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栈（stack）是先进后出的数据结构。单调栈在入栈时通过一定规则保持栈内元素有序（单调递增或单调递减），从而把「找左侧/右侧第一个更大/更小元素」从 O(n²) 降到 O(n)。
odd positions: 9,7,5,3,1 sum to 25;