# TreeMap (Condensed Guide)

## What Is TreeMap?

`TreeMap` is a `Map` implementation that stores key-value pairs in **sorted order based on the keys**.

It:
- Stores data as **key-value pairs**
- Automatically **sorts keys**
- Does **not allow null keys**
- Allows multiple null values

```java
import java.util.Map;
import java.util.TreeMap;

Map<String, Integer> scores = new TreeMap<>();

Map
 ↓
SortedMap
 ↓
NavigableMap
 ↓
TreeMap

TreeMap implements both SortedMap and NavigableMap.

TreeMap is implemented using a Red-Black Tree, a type of self-balancing binary search tree.

This means:

• Keys are always stored in sorted order
• Insertions maintain tree balance
• Lookups are efficient but slower than HashMap

Sorting can occur:

• Using natural ordering (e.g., alphabetical, numerical)
• Using a custom comparator

TreeMap is slower than HashMap because it maintains sorting.

map.put("Alice", 90);
map.put("Bob", 85);
map.put("Charlie", 92);

Keys will automatically appear in sorted order.

map.get("Alice");

map.remove("Bob");

map.containsKey("Alice");

map.size();

map.firstKey();
map.lastKey();

map.subMap("A", "M");

Returns keys between "A" and "M".

map.higherKey("Bob");   // next higher key
map.lowerKey("Bob");    // next lower key

map.ceilingKey("Bob");  // smallest key >= "Bob"
map.floorKey("Bob");    // largest key <= "Bob"

for (Map.Entry<String, Integer> entry : map.entrySet()) {
    System.out.println(entry.getKey() + " -> " + entry.getValue());
}

Output will always be sorted by key.

Use TreeMap when:

• You need sorted keys
• You need range queries
• You need ordered iteration

Examples:

• Leaderboards
• Sorted indexes
• Time-based event storage
• Range searching

Map<Integer, String> students = new TreeMap<>();

students.put(3, "Alice");
students.put(1, "Bob");
students.put(2, "Charlie");

System.out.println(students);

Output:

{1=Bob, 2=Charlie, 3=Alice}

Keys are automatically sorted.

• Store numbers and return them in sorted order
• Build a leaderboard sorted by score
• Find the closest value to a target number
• Return elements in a range using subMap()

TreeMap is a sorted map implementation backed by a balanced tree.

Key characteristics:

• Keys automatically sorted
• O(log n) operations
• Supports range queries and navigation methods

Use TreeMap when ordered keys or range operations are required.