Constructs an empty container using `a` as the allocator and a maximum load factor of 1.0 and inserts the elements from `il` into it.
Constructs an empty container using `a` as the allocator and a maximum load factor of 1.0 and inserts the elements from `il` into it.使用 `a` 作为分配器构造一个空容器，设置最大负载因子为 1.0，并将 `il` 中的元素插入其中。
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Constructs an empty container using `a` as the allocator and a maximum load factor of 1.0 and inserts the elements from `il` into it.使用 `a` 作为分配器构造一个空容器，设置最大负载因子为 1.0，并将 `il` 中的元素插入其中。