**Set - Google Top Interview Questions**

### Problem Statement :

Implement a set data structure with the following methods: CustomSet() constructs a new instance of a set add(int val) adds val to the set exists(int val) returns whether val exists in the set remove(int val) removes the val in the set This should be implemented without using built-in set. Constraints n ≤ 100,000 where n is the number of calls to add, exists and remove Example 1 Input methods = ["constructor", "add", "exists", "remove", "exists"] arguments = [[], [1], [1], [1], [1]]` Output [None, None, True, None, False] Explanation c = CustomSet() c.add(1) c.exists(1) == True c.remove(1) c.exists(1) == False

### Solution :

` ````
Solution in C++ :
class CustomSet {
int S = 1e3;
vector<list<int>> v;
hash<int> hs;
public:
CustomSet() {
v.resize(S);
}
void add(int val) {
if (exists(val)) return;
int id = hs(val) % S;
v[id].push_back(val);
}
bool exists(int val) {
int id = hs(val) % S;
for (int x : v[id]) {
if (x == val) return true;
}
return false;
}
void remove(int val) {
int id = hs(val) % S;
for (auto it = v[id].begin(); it != v[id].end(); it++) {
if (*it == val) {
v[id].erase(it);
return;
}
}
}
};
```

` ````
Solution in Java :
import java.util.*;
class CustomSet {
ArrayList<Integer>[] buckets;
int T;
public CustomSet() {
T = 300;
buckets = new ArrayList[T];
}
public void add(int val) {
if (!exists(val)) {
buckets[map(val)].add(val);
}
}
public boolean exists(int val) {
int m = map(val);
if (buckets[m] == null)
buckets[m] = new ArrayList<Integer>();
return buckets[m].contains(val);
}
public void remove(int val) {
if (exists(val))
buckets[map(val)].remove(Integer.valueOf(val));
}
public int map(int val) {
return ((val % T) + T) % T;
}
}
```

` ````
Solution in Python :
class ListNode:
def __init__(self, val):
self.val = val
self.next = None
class CustomSet:
def __init__(self):
self.mod = 2069 # any large prime number
self.lst = [None] * self.mod
def add(self, val):
hashkey = val % self.mod
if not self.lst[hashkey]:
self.lst[hashkey] = ListNode(val)
else:
curr = self.lst[hashkey]
while curr.next:
if curr.val == val:
return
curr = curr.next
if curr.val == val:
return
curr.next = ListNode(val)
def exists(self, val):
hashkey = val % self.mod
if self.lst[hashkey]:
curr = self.lst[hashkey]
while curr:
if curr.val == val:
return True
curr = curr.next
return False
def remove(self, val):
hashkey = val % self.mod
if self.lst[hashkey]:
curr = self.lst[hashkey]
if curr.val == val:
self.lst[hashkey] = curr.next
return
while curr.next:
if curr.next.val == val:
curr.next = curr.next.next
return
curr = curr.next
```

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