Java内置函数Collections.frequency(list,element)的复杂性是什么? [英] What is the Complexity of the Java's in-built function Collections.frequency(list, element)?
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问题描述
下面的代码用于String的ArrayList。我想知道 Collections.frequency()
函数的复杂性。
The code below is for the ArrayList of String. I want to know what's the complexity of the Collections.frequency()
function.
List<String> list = new ArrayList<>();
list.add("sample");
list.add("sample1");
list.add("sample");
list.add("sample");
list.add("sample");
list.add("sample");
System.out.println("sample is repeated : " + Collections.frequency(list, "sample"));
推荐答案
Collections.frequency
具有以下实现(在Java 9中):
Collections.frequency
has the following implementation (in Java 9):
public static int frequency(Collection<?> c, Object o) {
int result = 0;
if (o == null) {
for (Object e : c)
if (e == null)
result++;
} else {
for (Object e : c)
if (o.equals(e))
result++;
}
return result;
}
因此它是 O(n)
。
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