Design HashMap

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

To be specific, your design should include these functions:

• `put(key, value)` : Insert a (key, value) pair into the HashMap. If the value already exists in the HashMap, update the value.
• `get(key)` : Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
• `remove(key)` : Remove the mapping for the value key if this map contains the mapping for the key.

Example:

``````MyHashMap hashMap = new MyHashMap();
hashMap.put(1, 1);
hashMap.put(2, 2);
hashMap.get(1);            // returns 1
hashMap.put(2, 1);          // update the existing value
hashMap.get(2);            // returns 1
hashMap.remove(2);          // remove the mapping for 2
``````

Note:

• All keys and values will be in the range of `[0, 1000000]`.
• The number of operations will be in the range of `[1, 10000]`.
• Please do not use the built-in HashMap library.

## Solution

``````import javafx.util.Pair;

class MyHashMap {
private final int MAX_LEN = 100000;             // the amount of buckets
private List<Pair<Integer, Integer>>[] map;     // hash map implemented by array

/** Returns the corresponding bucket index. */
private int getIndex(int key) {
return key % MAX_LEN;
}

/** Search the key in a specific bucket. Returns -1 if the key does not existed. */
private int getPos(int key, int index) {
// Each bucket contains a list.
List<Pair<Integer, Integer>> temp = map[index];
if (temp == null) {
return -1;
}
// Iterate all the elements in the bucket to find the target key.
for (int i = 0; i < temp.size(); ++i) {
if (temp.get(i).getKey() == key) {
return i;
}
}
return -1;
}

/** Initialize your data structure here. */
public MyHashMap() {
map = (List<Pair<Integer, Integer>>[])new ArrayList[MAX_LEN];
}

/** value will always be positive. */
public void put(int key, int value) {
int index = getIndex(key);
int pos = getPos(key, index);
if (pos < 0) {
// Add new (key, value) pair if key is not existed.
if (map[index] == null) {
map[index] = new ArrayList<Pair<Integer, Integer>>();
}
} else {
// Update the value if key is existed.
map[index].set(pos, new Pair(key, value));
}
}

/** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
public int get(int key) {
int index = getIndex(key);
int pos = getPos(key, index);
if (pos < 0) {
return -1;
} else {
return map[index].get(pos).getValue();
}
}

/** Removes the mapping of the specified value key if this map contains a mapping for the key */
public void remove(int key) {
int index = getIndex(key);
int pos = getPos(key, index);
if (pos >= 0) {
map[index].remove(pos);
}
}
}

/**
* 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);
*/
``````