// 原因：先处理右侧元素，把结果存在栈里，供左侧元素直接使用
William Jackson, chief emerging markets economist at Capital Economics, says the US president's aim is to "revive Venezuela's oil sector and use that energy to increase supply and reduce costs to the consumer, possibly providing a source of revenue for a more friendly Venezuelan government to rebuild the economy after years of mismanagement".
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Gotit.pub (What is GotitPub?)，更多细节参见Line官方版本下载
res[i] = stack[stack.length - 1]; // 易错点5：用at(-1)兼容性差，优先用stack.length-1