[英]Fastest way to check if value is in array many times
I have an array of some values between -15
and 31
and I have to check, if some x
is in this array for ~300 000 000
times. 我有一些介于
-15
和31
之间的值的数组,我必须检查,如果某个x
在这个数组中~300 000 000
次。 Because there is negative values, I can't create boolean array. 因为有负值,我无法创建布尔数组。 Now I am creating
HashSet
from original array and use .contains()
method, but this is too slow. 现在我从原始数组创建
HashSet
并使用.contains()
方法,但这太慢了。 Is there any faster way or trick? 有没有更快的方法或技巧?
Update I create this array from another one (so I can use any structure I want) 更新我从另一个创建这个数组(所以我可以使用我想要的任何结构)
You could easily create a boolean
array and just offset the index: 您可以轻松创建一个
boolean
数组,只是偏移索引:
// Do this once...
int minValueInclusive = -15;
int maxValueExclusive = 31;
boolean[] presence = new boolean[maxValueExclusive - minValueInclusive + 1];
for (int value : array) {
presence[value - minValueInclusive] = true;
}
Then to check for presence: 然后检查是否存在:
if (presence[index - minValueInclusive]) {
...
}
Alternatively, as you're using fewer than 64 bits you could store the whole thing in a single long
, and use bitshifting. 或者,当您使用少于64位时,您可以将整个事物存储在一个
long
整数中,并使用位移。
// Do this once...
int minValueInclusive = -15;
long presence = 0;
for (int value : array) {
presence |= 1L << (value - minValueInclusive);
}
Then to check for presence: 然后检查是否存在:
if ((presence & (1L << (index - minValueInclusive))) != 0) {
...
}
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