clarkzhao / LeetcodeSolution

LeetcodeSolution

This solution is written in Python at first.

• python

• C++

• Java

Menu

Squence	Name of Problem	Tags	Level	Language
1	Two Sum	Array, Hash Table	Easy	Python
167	Two Sum II - input array is sorted	Array, Two pointer, Binary Search	Medium	Python
238	Product of Array Except Self	Array	Medium	python
283	Move Zeroes	Array, Two pointers	Easy	python
442	Find All Duplicates in an Array	Array	Medium	[python]((https://github.com/clarkzhao/LeetcodeSolution/blob/master/src/find_all_duplicates_in_an_array.py)
448	Find All Numbers Disappeared in an Array	Array	Easy	Python

Notes

Two Sum

• Compared to brute force solution, the use of hash_map (Dictionary in python) is more efficient.
• hash_map[residual] is returned at first, because the expected result is in ascending order.

Two Summ II

• Take the advantage of the ascending order of the input array.
• The least complexity is O(N) using two pointer
• Binary search has a complexity of O(N*log(N))

Product of Array Except Self

• It is easy to know by intuition, we cannot finish this task within one for loop.
• For example, assuming the input is [1,2,3,4]:

iteration	output[0]	output[1]	output[2]	output[3]
0	x1	x1	x1	x1
1	x2	x1	x2	x2
2	x3	x3	x1	x3
3	x4	x4	x4	x1
output	24	12	8	6

• Notice that, output[i] is multiplied by 1 for iteration 1
• For the first loop, we get the information in the upper right of above table that is [1, 1x1, 1x2, 1x2x3] which is [1, 1, 2, 6]
• For the second loop, we get the information in the lower left of above table that is [4x3x2, 4x3, 4, 1] which is [24, 12, 4, 1]
• The results is just the product of the items in the two list.

Move zeroes

• At first, I misunderstand the question. I thought the requirements is to put all the zeros in front of the arrays. That's Why I have the last line in first solution
• The second solution and similar solution puts my solution to shame. The reason is that I use insert method of python List and so less efficient.

Find All Duplicates in an Array

• This is question similar to Question 448. My solution use extra O(n) spaces, while this solution use the tricks that the absolute value of the one value and its negativity are the same to avoid using extra spaces.

Find All Numbers Disappeared in an Array

• Take the advantage of using the value of one array as the index for an array.
• One solution marks the value by taking negative of them, and get the value by taking absolute of them, and it saves extra spaces than my solution.
• Another solution tries to solve similar problem but using concept of remainder.