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Wenqi Jiang
Wenqi Jiang

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705. Design HashSet

705. Design HashSet

Description

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)
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Constraints:

  • 0 <= key <= 106
  • At most 104 calls will be made to addremove, and contains.

Solutions

Solution 1

Intuition

Code

const int N = 113;
class MyHashSet {
private:
    vector<int> mySet[N];
    int find(int linkIndex, int target) {
        vector<int> &link = mySet[linkIndex];
        for (int i = 0; i < link.size(); i++) {
            if (link[i] == target) return i;
        }
        return -1;
    }

public:
    MyHashSet() {
    }

    void add(int key) {
        int linkIndex = key % N;
        int index = find(linkIndex, key);
        if (index == -1) mySet[linkIndex].push_back(key);
    }

    void remove(int key) {
        int linkIndex = key % N;
        int index = find(linkIndex, key);
        if (index != -1) mySet[linkIndex].erase(mySet[linkIndex].begin() + index);
    }

    bool contains(int key) {
        int linkIndex = key % N;
        int index = find(linkIndex, key);
        return index != -1;
    }
};

/**
 * Your MyHashSet object will be instantiated and called as such:
 * MyHashSet* obj = new MyHashSet();
 * obj->add(key);
 * obj->remove(key);
 * bool param_3 = obj->contains(key);
 */
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Complexity

  • Time: O(n)
  • Space: O(n)

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