706. Design HashMap
1. Description
Design a HashMap without using any built-in hash table libraries.
Implement the MyHashMap class:
- MyHashMap() initializes the object with an empty map.
- void put(int key, int value) inserts a (key, value) pair into the HashMap. If the key already exists in the map, update the corresponding value.
- int get(int key) returns the value to which the specified key is mapped, or -1 if this map contains no mapping for the key.
- void remove(key) removes the key and its corresponding value if the map contains the mapping for the key.
2. Example
Example 1:
Input
[“MyHashMap”, “put”, “put”, “get”, “get”, “put”, “get”, “remove”, “get”]
[[], [1, 1], [2, 2], [1], [3], [2, 1], [2], [2], [2]]
Output
[null, null, null, 1, -1, null, 1, null, -1]
Explanation
MyHashMap myHashMap = new MyHashMap();
myHashMap.put(1, 1); // The map is now [[1,1]]
myHashMap.put(2, 2); // The map is now [[1,1], [2,2]]
myHashMap.get(1); // return 1, The map is now [[1,1], [2,2]]
myHashMap.get(3); // return -1 (i.e., not found), The map is now [[1,1], [2,2]]
myHashMap.put(2, 1); // The map is now [[1,1], [2,1]] (i.e., update the existing value)
myHashMap.get(2); // return 1, The map is now [[1,1], [2,1]]
myHashMap.remove(2); // remove the mapping for 2, The map is now [[1,1]]
myHashMap.get(2); // return -1 (i.e., not found), The map is now [[1,1]]
3. Constraints
- 0 <= key, value <= $10^6$
- At most 104 calls will be made to put, get, and remove.
4. Follow Up
Please do not use the built-in HashMap library.
5. Solutions
My Accepted Solution(Follow Up)
n = i_nums.size()
Time complexity: O(n)
Space complexity: O(n)
class MyHashMap
{
public:
/** Initialize your data structure here. */
MyHashMap()
{
data = vector<vector<pair<int, int>>>(g_hashSize);
}
/** value will always be non-negative. */
void put(int key, int value)
{
int index = key % g_hashSize;
auto keyIter = find_if(data[index].begin(), data[index].end(), [key](pair<int, int> iter) { return iter.first == key; });
if (keyIter == data[index].end())
{
data[index].push_back(pair<int, int>(key, value));
}
else
{
*keyIter = pair<int, int>(key, value);
}
}
/** 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 index = key % g_hashSize;
auto keyIter = find_if(data[index].begin(), data[index].end(), [key](pair<int, int> iter) { return iter.first == key; });
return keyIter == data[index].end() ? -1 : (*keyIter).second;
}
/** Removes the mapping of the specified value key if this map contains a mapping for the key */
void remove(int key)
{
int index = key % g_hashSize;
auto keyIter = find_if(data[index].begin(), data[index].end(), [key](pair<int, int> iter) { return iter.first == key; });
if (keyIter != data[index].end())
{
data[index].erase(keyIter);
}
}
private:
const int g_hashSize = 1009; // it should be a prime, which could help us reducing conflicts
vector<vector<pair<int, int>>> data;
};