2021-04-29 09:16:40 +00:00
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# 数组
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2021-04-01 01:06:07 +00:00
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* 计算给定数组 arr 中所有元素的总和
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输入 [ 1, 2, 3, 4 ]
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输出： 10
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* 找出数组 arr 中重复出现过的元素
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输入[1, 2, 4, 4, 3, 3, 1, 5, 3]
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输出：[1, 3, 4]
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* 写一个函数 统计数组 arr 中值等于 item 的元素出现的次数
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输入： [1, 2, 4, 4, 3, 4, 3], 4
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输出：3
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* 给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。答案可以按 任意顺序 返回。
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给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。
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输入：digits = "23"
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输出：["ad","ae","af","bd","be","bf","cd","ce","cf"]
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