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【LeetCode】705. Design HashSet 解题报告(Python)


id: fuxuemingzhu

个人博客: ​​​http://fuxuemingzhu.cn/​​​


目录


  • ​​题目描述​​
  • ​​题目大意​​
  • ​​解题方法​​

  • ​​位图法​​
  • ​​数组法​​

  • ​​日期​​


题目地址:​​https://leetcode.com/problems/design-hashset/description/​​

题目描述

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

To be specific, your design should include these two functions:


  • ​add(value)​​: Insert a value into the HashSet.
  • ​contains(value)​​ : Return whether the value exists in the HashSet or not.
  • ​remove(value)​​: Remove a value in the HashSet. If the value does not exist in the HashSet, do nothing.

Example:

MyHashSet hashSet = new MyHashSet();
hashSet.add(1);
hashSet.add(2);
hashSet.contains(1); // returns true
hashSet.contains(3); // returns false (not found)
hashSet.add(2);
hashSet.contains(2); // returns true
hashSet.remove(2);
hashSet.contains(2); // returns false (already removed)

Note:


  • All values will be in the range of [1, 1000000].
  • The number of operations will be in the range of [1, 10000].
  • Please do not use the built-in HashSet library.

题目大意

动手实现一个hashset.不能用已经内置的函数。

解题方法

位图法

那么直接想到能不能真正模拟hashset呢?通过计算hash,或者一个元素一个坑的方法进行模拟?

参考了一下别人的代码,比我想的要机智一点。这个思路的方法是第一个维度只做hash,第二个维度保存具体元素。这个思想类似于HashMap中的bucket+链表桶。

我觉得这个方法最大的优点就是省内存,因为这种设计当需要的时候,才会产生第二个维度的数据。

代码如下:

class MyHashSet:

def __init__(self):
"""
Initialize your data structure here.
"""
self.buckets = 1000
self.itemsPerBucket = 1001
self.table = [[] for _ in range(self.buckets)]

def hash(self, key):
return key % self.buckets

def pos(self, key):
return key // self.buckets

def add(self, key):
"""
:type key: int
:rtype: void
"""
hashkey = self.hash(key)
if not self.table[hashkey]:
self.table[hashkey] = [0] * self.itemsPerBucket
self.table[hashkey][self.pos(key)] = 1

def remove(self, key):
"""
:type key: int
:rtype: void
"""
hashkey = self.hash(key)
if self.table[hashkey]:
self.table[hashkey][self.pos(key)] = 0

def contains(self, key):
"""
Returns true if this set did not already contain the specified element
:type key: int
:rtype: bool
"""
hashkey = self.hash(key)
return (self.table[hashkey] != []) and (self.table[hashkey][self.pos(key)] == 1)

# Your MyHashSet object will be instantiated and called as such:
# obj = MyHashSet()
# obj.add(key)
# obj.remove(key)
# param_3 = obj.contains(key)

数组法

直接开辟这么大的一个数组,然后全部设置成False,哪里有数字哪里就是True。空间没有超。

class MyHashSet:

def __init__(self):
"""
Initialize your data structure here.
"""
self.set = [False] * 1000001

def add(self, key):
"""
:type key: int
:rtype: void
"""
self.set[key] = True

def remove(self, key):
"""
:type key: int
:rtype: void
"""
self.set[key] = False

def contains(self, key):
"""
Returns true if this set contains the specified element
:type key: int
:rtype: bool
"""
return self.set[key]


# Your MyHashSet object will be instantiated and called as such:
# obj = MyHashSet()
# obj.add(key)
# obj.remove(key)
# param_3 = obj.contains(key)

日期

2018 年 7 月 12 日 —— 天阴阴地潮潮,已经连着两天这样了

2018 年 11 月 17 日 —— 美妙的周末,美丽的天气



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