边工作边刷题：70天一遍leetcode: day 71-3

Two Sum I/II/III

要点：都是简单题，III就要注意如果value-num==num的情况，所以要count，并且count>1
https://repl.it/CrZG
错误点：

• TLE：defaultdict is slower than normal dict
• TLE：.keys() copies keys, it’s way slower

# Design and implement a TwoSum class. It should support the following operations: add and find.

# add - Add the number to an internal data structure.
# find - Find if there exists any pair of numbers which sum is equal to the value.

# For example,
# add(1); add(3); add(5);
# find(4) -> true
# find(7) -> false
# Hide Company Tags LinkedIn
# Hide Tags Hash Table Design
# Hide Similar Problems (E) Two Sum (E) Unique Word Abbreviation

from collections import defaultdict

class TwoSum(object):

    def __init__(self):
        """
        initialize your data structure here
        """
        self.counts = defaultdict(int)

    def add(self, number):
        """
        Add the number to an internal data structure.
        :rtype: nothing
        """
        self.counts[number]+=1

    def find(self, value):
        """
        Find if there exists any pair of numbers which sum is equal to the value.
        :type value: int
        :rtype: bool
        """
        for k in self.counts.keys():
            if value-k not in self.counts or (k==value-k and self.counts[k]==1):
                continue
            return True
        return False

# Your TwoSum object will be instantiated and called as such:
# twoSum = TwoSum()
# twoSum.add(number)
# twoSum.find(value)