leetcode 706 - Design HashMap

https://leetcode.com/problems/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.get(3); // returns -1 (not found)
hashMap.put(2, 1); // update the existing value
hashMap.get(2); // returns 1
hashMap.remove(2); // remove the mapping for 2
hashMap.get(2); // returns -1 (not found)

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.

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class MyHashMap {
public:
struct Element {
int key;
int value;
Element *next;

Element(int k, int v) {
key = k;
value = v;
next = NULL;
}
};

#define NUM_SLOTS 10000

vector<Element *> slots;

/** Initialize your data structure here. */
MyHashMap() {
slots.resize(NUM_SLOTS, NULL);
}

int slot(int key) {
return key % NUM_SLOTS;
}

/** value will always be non-negative. */
void put(int key, int value) {
int idx = slot(key);

Element *head = slots[idx];
while (head) {
if (head->key == key) {
head->value = value;
return;
}

head = head->next;
}

Element *e = new Element(key, value);
e->next = slots[idx];
slots[idx] = e;
}

/** Returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key */
int get(int key) {
int idx = slot(key);

Element *head = slots[idx];
while (head) {
if (head->key == key)
return head->value;
head = head->next;
}

return -1;
}

/** Removes the mapping of the specified value key if this map contains a mapping for the key */
void remove(int key) {
int idx = slot(key);

Element *head = slots[idx];
Element *prev = NULL;

while (head) {
if (head->key == key) {
if (prev) {
prev->next = head->next;
} else {
slots[idx] = head->next;
}

delete head;
return;
}

prev = head;
head = head->next;
}
}
};

/**
* 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);
*/