# Set - Google Top Interview Questions

### Problem Statement :

```Implement a set data structure with the following methods:

CustomSet() constructs a new instance of a 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.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);
}

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];
}

if (!exists(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

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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