当数组的元素个数发生变化时，不用重新申请内存空间，数组也能继续使用。这样就提高了效率。



对于机器算法中，“时间”和“空间”的矛盾总是存在的：存储多一点，运行就快些；存储少了，运行就慢些。在这里就体现了，这样处理是用空间换时间。虽然在内存空间上是“浪费”了部分的空间，但是在很长一段时间里，只要空间没有发生变化，运行的时间复杂度就恒定的。只有当现有的空间不够用时，才发生内存的重新申请和释放操作。最简单的增长方法就是增长一倍，即乘以2，这样内存分配的大小就是2的幂次方。

-When the number of elements in the array change, do not re-apply for the memory space, the array can continue to use. This will improve efficiency.



Algorithm for the machine, the "time" and "space" of the conflict is always there: a little more storage, running on the faster　store less, running on more slowly. Embodied in here, this treatment is a space for time. Although the memory space is "wasted" some of the space, but in a very long time, as long as the space has not changed, run on a constant time complexity. Only when existing space is not enough, the only place to re-apply and release the memory operation. The easiest way is to double the growth, that is multiplied by 2, so the size of memory allocation is a power of 2.