python

Leet Code 75

#	Problem Name	Solution	Description
1	Two Sum	Solution	Use a hash map to keep track of seen numbers
121	Best Time to Buy and Sell Stocks	Solution	Iterate over prices, if found lower price update buy date else keep searching for better profit
217	Contains Duplicate	Solution	Compare len of array vs len of set; alternatively add elements to set if element already seen return true
238	Product of Array Except Self	Solution	Calculate Prefix on one pass and then multiple with postfix on next pass
53	Maximum Subarray	Solution	Iterate while keeping track of cur sum, if it is negative discard it then start cur sum again. Take maximum of cur sum and maximum sum seen so far
152	Maximum Product Subarray	Solution	Iterate while keeping a curmin and curmax, update it when seeing a number, negative x negative will update in max being updated
153	Find minimum in Rotated Sorted Array	Solution	Set left to first element, right to last value, find middle. If middle is smaller than left than search left else search right
33	Search in rotated sorted array	Solution	Use middle to find if you're in the left part of the sorted array or the right part, then update search area based on the middle value and the extreme value
15	3Sum	Solution	O(n2): Sort the array, Fix a starting point then look for left and right, if total > 0, move right inwards, else if target < 0, move left outwards, otherwise move to next fixed number
11	Container with Most Water	Solution	Two pointer solution, start with extremes move whichever side is lower to the opposite side
191	Number of 1 Bits	Solution	Mod number with 2, then keep count, shift number using bit shift operator
338	Counting Bits	Solution	Dynamic Programming, keep an offset (power of two) and for every number find significant digit and add 1 for that and resst is the same number of bits as number - offset, eg: 7 = 1 + same as 4
268	Missing Number	Solution	Subtract from sub of n numbers formula or xor with every number in that range
190	Reverse Bits	Solution	Iterate over length, find ith bit by doing and, shift that by n - i and or it with result
70	Climbing Stairs	Solution	Fibonnaci Series Sum, keep track of last two step solutions, set the preceding solution to the sum of the two
322	Coin Change	Solution	Dynamic Programming: For each amount in range(1, amount+1), the solution = 1 + cur_amount - coin for every coin and then take the minimum
300	Longest Increasing Subsequence	Solution	Dynamic Programming, starting with the last element try to add elements
1143	Longest Common Subsequence	Solution
242	Valid Anagram	Solution	Create a hash map of the counts for each character, or sort the strings
167	Two Sum II	Solution	Left and right pointers, if too high move right to the center, if too low move left to the center
198	House Robbers	Solution	Maintain house 1 and house 2, update house1 to house 2, and house2 to max(house1+n, house2)
235	Lowest Common Ancestor of a Binary Tree	Solution	Three cases: Either the values are split, then root is the LCA otherwise search left or right based on values
202	Happy Number	Solution	Keep a set to track numbers already visited, loop
155	Min Stack	Solution	Keep a second list / or track of mins at every point
203	Remove Linked List Element	Solution	Move the head till we keep getting the target val then remove from the rest of the list while tracking prev node
35	Search Insert Position	Solution	Binary search, return position based on target vs left / right
1046	Last Stone Weight	Solution	Heapify the stones list, python only has min heap so multiply everything by a -1 to get max heap
26	Remove Duplicates from Sorted Array	Solution	Keep a pointer to track unique values, iterate and replace at pointer spot
263	Ugly Number	Solution	Keep dividing by the specified prime numbers while it is divisible, if at the end n=1 then return true else false
58	Length of Last Word	Solution	.split() recognizes words, then check len of last element
929	Unique Email Addresses	Solution
929	Two Sum - Alternate	Solution
929	Map Reduce	Solution
929	Sort Version Number	Solution