706. Design HashMap

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# 題目敘述

Design a HashMap without using any built-in hash table libraries.

Implement the MyHashMap class:

• MyHashMap() initializes the object with an empty map.
• void put(int key, int value) inserts a (key, value) pair into the HashMap. If the key already exists in the map, update the corresponding value .
• int get(int key) returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key .
• void remove(key) removes the key and its corresponding value if the map contains the mapping for the key .

# Example 1

Input
["MyHashMap", "put", "put", "get", "get", "put", "get", "remove", "get"]
[[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
Output
[null, null, null, 1, -1, null, 1, null, -1]

Explanation
MyHashMap myHashMap = new MyHashMap();
myHashMap.put(1, 1); // The map is now [[1,1]]
myHashMap.put(2, 2); // The map is now [[1,1], [2,2]]
myHashMap.get(1); // return 1, The map is now [[1,1], [2,2]]
myHashMap.get(3); // return -1 (i.e., not found), The map is now [[1,1], [2,2]]
myHashMap.put(2, 1); // The map is now [[1,1], [2,1]] (i.e., update the existing value)
myHashMap.get(2); // return 1, The map is now [[1,1], [2,1]]
myHashMap.remove(2); // remove the mapping for 2, The map is now [[1,1]]
myHashMap.get(2); // return -1 (i.e., not found), The map is now [[1,1]]

# 解題思路

# Solution

import java.util.HashMap;

import java.util.Map;

class MyHashMap {

    Map<Integer, Integer> map;

    public MyHashMap() {

        map = new HashMap<>();

    }

    public void put(int key, int value) {

        map.put(key, value);

    }

    public int get(int key) {

        return map.getOrDefault(key, -1);

    }

    public void remove(int key) {

        map.remove(key);

    }

}

/**

 * Your MyHashMap object will be instantiated and called as such:

 * MyHashMap obj = new MyHashMap();

 * obj.put(key,value);

 * int param_2 = obj.get(key);

 * obj.remove(key);

 */