Today I have done leetcode's April LeetCoding Challenge with cpp.

April LeetCoding Challenge 21

Description

Design HashSet

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

Implement MyHashSet class:

• void add(key) Inserts the value key into the HashSet.
• bool contains(key) Returns whether the value key exists in the HashSet or not.
• void remove(key) Removes the value key in the HashSet. If key does not exist in the HashSet, do nothing.

Example 1:

Input
["MyHashSet", "add", "add", "contains", "contains", "add", "contains", "remove", "contains"]
[[], [1], [2], [1], [3], [2], [2], [2], [2]]
Output
[null, null, null, true, false, null, true, null, false]

Explanation
MyHashSet myHashSet = new MyHashSet();
myHashSet.add(1);      // set = [1]
myHashSet.add(2);      // set = [1, 2]
myHashSet.contains(1); // return True
myHashSet.contains(3); // return False, (not found)
myHashSet.add(2);      // set = [1, 2]
myHashSet.contains(2); // return True
myHashSet.remove(2);   // set = [1]
myHashSet.contains(2); // return False, (already removed)

Constraints:

• 0 <= key <= 10^6
• At most 10^4 calls will be made to add, remove, and contains.

Solution

constexpr int MOD = 4001;
class MyHashSet {
  vector<vector<int>> container;
public:
  MyHashSet(): container(MOD) {}
  
  void add(int key) {
    int val = key;
    key %= MOD;
    for(auto v : container[key]) {
      if(v == val) return;
    }
    container[key].push_back(val);
  }
  
  void remove(int key) {
    int val = key;
    key %= MOD;
    auto it = container[key].begin();
    while(it != container[key].end() && *it != val) {
      ++it;
    }
    if(it != container[key].end()) {
      container[key].erase(it);
    }
  }
  
  bool contains(int key) {
    int val = key;
    key %= MOD;
    for(auto v : container[key]) {
      if(v == val) return true;
    }
    return false;
  }
};

// Accepted
// 32/32 cases passed (93 ms)
// Your runtime beats 87.94 % of cpp submissions
// Your memory usage beats 39.75 % of cpp submissions (43.9 MB)