Find the Biggest number in HashSet/HashMap java

Question

I would like to find the biggest number in HashSet and HashMap. Say I have the number [22,6763,32,42,33] in my HashSet and I want to find the largest number in my current HashSet..how would i do this? and Same thing for the HashMap as well. I hope you can help me with it. Thank you.

Solution 1

You can use Collections.max(Collection) to find the maximum element out of any collection. Similarly, for a HashMap, you can use the same method on its keySet() or values(), depending upon whether you want maximum key, or maximum value.

Also, if you want as such, you can use a TreeSet and TreeMap instead, that stores the elements in sorted key order.

Solution 2

try

    int max = Collections.max(set);
    int maxKey = Collections.max(map.keySet());
    int maxValue Collections.max(map.values());

Solution 3

If you are forced to use a HashSet/HashMap, then you have to scan the whole HashSet/HashMap in order to find the maximum. Library functions like Collections.max() will do like this.

If you want O(1) retrieval of the maximum, and you are allowed to change the type of collection being used, use a sorted set/map (e.g. TreeSet/TreeMap).

Solution 4

Something like this:

Set<Integer> values = new HashSet<Integer>() {{
    add(22);
    add(6763);
    add(32);
    add(42);
    add(33);
}};
int maxValue = Integer.MIN_VALUE;
for (int value : values) {
    if (value > maxValue) {
        maxValue = value;
    }
}

And this:

Map<String, Integer> values = new HashMap<String, Integer>() {{
    put("0", 22);
    put("1", 6763);
    put("2", 32);
    put("3", 42);
    put("4", 33);
}};
int maxValue = Integer.MIN_VALUE;
for (int value : values.values()) {
    if (value > maxValue) {
        maxValue = value;
    }
}

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Comments

[David Schwartz]

If you need to do this, you probably shouldn't be using a hash-based collection.

[Marko Topolnik]

O(1) works only on map keys; for values a separate collection must be constructed first, so it's O(n) again, with a very bad constant factor.

[user2064467]

Wow..Thank you..it helps alot.:)

[Shiva Kumar]

Also note that TreeSet gets costlier for insertion and deletion. So wisely choose the right implementation

[Kamil]

Terrible way to initialize a HashMap just for that simple purpose a new class has to be created. I hate it every time I see it in code I work with.

[duffymo]

What's so terrible? I see no harm in it.

[Kamil]

What I wrote above, it creates new class just for the purpose of creating map with few elements. It's very slow (there are tests on it on stackoverflow).

[duffymo]

I'll never believe that this would be the bottleneck in any app. Micro-optimization at its worst.

[gladed]

Don't forget that max() throws NoSuchElementException on empty collections.