docs: update readme

Author: austingebauer

.gitignore

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+bin

Makefile

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+# Targets not related to individual files
+.PHONY: all test cover_func cover_html out clean vet loc fmt test_v bench
+
+BUILD_OUT_DIR = bin
+TEST_COVERAGE_PROFILE = coverage.out
+
+all: out fmt vet test_v loc solved
+
+out:
+	mkdir -p $(BUILD_OUT_DIR)
+
+fmt:
+	go fmt ./...
+
+vet:
+	go vet ./...
+
+test: out
+	go test -race ./... -coverprofile=$(BUILD_OUT_DIR)/$(TEST_COVERAGE_PROFILE)
+
+test_v: out
+	go test -race -v ./... -coverprofile=$(BUILD_OUT_DIR)/$(TEST_COVERAGE_PROFILE)
+
+bench:
+	go test -bench=.
+
+cover_func: test
+	go tool cover -func=$(BUILD_OUT_DIR)/$(TEST_COVERAGE_PROFILE)
+
+cover_html: test
+	go tool cover -html=$(BUILD_OUT_DIR)/$(TEST_COVERAGE_PROFILE)
+
+clean:
+	rm -rf $(BUILD_OUT_DIR)
+
+solved:
+	ls -ld -- */ | wc -l
+
+loc:
+	find . -type f -not -path "./vendor/*" -name "*.go" | xargs wc -l

README.md

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+# go-leetcode
+
+A collection of 100+ popular [LeetCode](https://leetcode.com/) problems solved in 
+[Go](https://golang.org/).
+
+Each directory includes a:
+- Description with link to LeetCode problem
+- Solution to the problem
+- A unit test
+
+Note that each of these problems **have passed** their respective test cases on LeetCode. The unit 
+tests included with each solution in this repo are not comprehensive. They serve as a quick way to 
+drop in a test case, hook up the debugger, and step through the algorithms to build understanding. 
+
+## Problems
+
+There are a variety of popular LeetCode problems solved in this repository. However, most of the problems
+solved are from a highly recommended, curated list of problems called 
+[Top 75 LeetCode Problems](https://www.teamblind.com/post/New-Year-Gift---Curated-List-of-Top-100-LeetCode-Questions-to-Save-Your-Time-OaM1orEU).
+
+The [Top 75 LeetCode Problems](https://www.teamblind.com/post/New-Year-Gift---Curated-List-of-Top-100-LeetCode-Questions-to-Save-Your-Time-OaM1orEU) 
+list is comprehensive, covering a decent breadth and depth for each category. Working through that list will certainly 
+help build the core concepts, techniques, and intuition needed to solve these types of problems.
+
+I've included a checklist that you can use to work through the list below:
+
+#### Array
+
+- [X] Two Sum - [https://leetcode.com/problems/two-sum/](https://leetcode.com/problems/two-sum/)  
+- [X] Best Time to Buy and Sell Stock - [https://leetcode.com/problems/best-time-to-buy-and-sell-stock/](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/)  
+- [X] Contains Duplicate - [https://leetcode.com/problems/contains-duplicate/](https://leetcode.com/problems/contains-duplicate/)  
+- [X] Product of Array Except Self - [https://leetcode.com/problems/product-of-array-except-self/](https://leetcode.com/problems/product-of-array-except-self/)  
+- [X] Maximum Subarray - [https://leetcode.com/problems/maximum-subarray/](https://leetcode.com/problems/maximum-subarray/)  
+- [X] Maximum Product Subarray - [https://leetcode.com/problems/maximum-product-subarray/](https://leetcode.com/problems/maximum-product-subarray/)  
+- [X] Find Minimum in Rotated Sorted Array - [https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/)  
+- [X] Search in Rotated Sorted Array - [https://leetcode.com/problems/search-in-rotated-sorted-array/](https://leetcode.com/problems/search-in-rotated-sorted-array/)  
+- [X] 3Sum - [https://leetcode.com/problems/3sum/](https://leetcode.com/problems/3sum/)  
+- [X] Container With Most Water - [https://leetcode.com/problems/container-with-most-water/](https://leetcode.com/problems/container-with-most-water/)
+
+---
+
+#### Binary
+
+- [X] Sum of Two Integers - [https://leetcode.com/problems/sum-of-two-integers/](https://leetcode.com/problems/sum-of-two-integers/)  
+- [X] Number of 1 Bits - [https://leetcode.com/problems/number-of-1-bits/](https://leetcode.com/problems/number-of-1-bits/)  
+- [X] Counting Bits - [https://leetcode.com/problems/counting-bits/](https://leetcode.com/problems/counting-bits/)  
+- [X] Missing Number - [https://leetcode.com/problems/missing-number/](https://leetcode.com/problems/missing-number/)  
+- [X] Reverse Bits - [https://leetcode.com/problems/reverse-bits/](https://leetcode.com/problems/reverse-bits/)
+
+---
+
+#### Dynamic Programming
+
+- [X] Climbing Stairs - [https://leetcode.com/problems/climbing-stairs/](https://leetcode.com/problems/climbing-stairs/)  
+- [X] Coin Change - [https://leetcode.com/problems/coin-change/](https://leetcode.com/problems/coin-change/)  
+- [X] Longest Increasing Subsequence - [https://leetcode.com/problems/longest-increasing-subsequence/](https://leetcode.com/problems/longest-increasing-subsequence/)  
+- [X] Longest Common Subsequence - [https://leetcode.com/problems/longest-common-subsequence/](https://leetcode.com/problems/longest-common-subsequence/)  
+- [X] Word Break Problem - [https://leetcode.com/problems/word-break/](https://leetcode.com/problems/word-break/)  
+- [X] Combination Sum - [https://leetcode.com/problems/combination-sum-iv/](https://leetcode.com/problems/combination-sum-iv/)  
+- [X] House Robber - [https://leetcode.com/problems/house-robber/](https://leetcode.com/problems/house-robber/)  
+- [X] House Robber II - [https://leetcode.com/problems/house-robber-ii/](https://leetcode.com/problems/house-robber-ii/)  
+- [X] Decode Ways - [https://leetcode.com/problems/decode-ways/](https://leetcode.com/problems/decode-ways/)  
+- [X] Unique Paths - [https://leetcode.com/problems/unique-paths/](https://leetcode.com/problems/unique-paths/)  
+- [X] Jump Game - [https://leetcode.com/problems/jump-game/](https://leetcode.com/problems/jump-game/)
+
+---
+
+#### Graph
+
+- [X] Clone Graph - [https://leetcode.com/problems/clone-graph/](https://leetcode.com/problems/clone-graph/)  
+- [X] Course Schedule - [https://leetcode.com/problems/course-schedule/](https://leetcode.com/problems/course-schedule/)  
+- [X] Pacific Atlantic Water Flow - [https://leetcode.com/problems/pacific-atlantic-water-flow/](https://leetcode.com/problems/pacific-atlantic-water-flow/)  
+- [X] Number of Islands - [https://leetcode.com/problems/number-of-islands/](https://leetcode.com/problems/number-of-islands/)  
+- [X] Longest Consecutive Sequence - [https://leetcode.com/problems/longest-consecutive-sequence/](https://leetcode.com/problems/longest-consecutive-sequence/)  
+- [X] Alien Dictionary (Leetcode Premium) - [https://leetcode.com/problems/alien-dictionary/](https://leetcode.com/problems/alien-dictionary/)  
+- [X] Graph Valid Tree (Leetcode Premium) - [https://leetcode.com/problems/graph-valid-tree/](https://leetcode.com/problems/graph-valid-tree/)  
+- [X] Number of Connected Components in an Undirected Graph (Leetcode Premium) - [https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/](https://leetcode.com/problems/number-of-connected-components-in-an-undirected-graph/)
+
+---
+
+#### Interval
+
+- [X] Insert Interval - [https://leetcode.com/problems/insert-interval/](https://leetcode.com/problems/insert-interval/)  
+- [X] Merge Intervals - [https://leetcode.com/problems/merge-intervals/](https://leetcode.com/problems/merge-intervals/)  
+- [X] Non-overlapping Intervals - [https://leetcode.com/problems/non-overlapping-intervals/](https://leetcode.com/problems/non-overlapping-intervals/)  
+- [X] Meeting Rooms (Leetcode Premium) - [https://leetcode.com/problems/meeting-rooms/](https://leetcode.com/problems/meeting-rooms/)  
+- [X] Meeting Rooms II (Leetcode Premium) - [https://leetcode.com/problems/meeting-rooms-ii/](https://leetcode.com/problems/meeting-rooms-ii/)
+
+---
+
+#### Linked List
+
+- [X] Reverse a Linked List - [https://leetcode.com/problems/reverse-linked-list/](https://leetcode.com/problems/reverse-linked-list/)  
+- [X] Detect Cycle in a Linked List - [https://leetcode.com/problems/linked-list-cycle/](https://leetcode.com/problems/linked-list-cycle/)  
+- [X] Merge Two Sorted Lists - [https://leetcode.com/problems/merge-two-sorted-lists/](https://leetcode.com/problems/merge-two-sorted-lists/)  
+- [X] Merge K Sorted Lists - [https://leetcode.com/problems/merge-k-sorted-lists/](https://leetcode.com/problems/merge-k-sorted-lists/)  
+- [X] Remove Nth Node From End Of List - [https://leetcode.com/problems/remove-nth-node-from-end-of-list/](https://leetcode.com/problems/remove-nth-node-from-end-of-list/)  
+- [X] Reorder List - [https://leetcode.com/problems/reorder-list/](https://leetcode.com/problems/reorder-list/)
+
+---
+
+#### Matrix
+
+- [X] Set Matrix Zeroes - [https://leetcode.com/problems/set-matrix-zeroes/](https://leetcode.com/problems/set-matrix-zeroes/)  
+- [X] Spiral Matrix - [https://leetcode.com/problems/spiral-matrix/](https://leetcode.com/problems/spiral-matrix/)  
+- [X] Rotate Image - [https://leetcode.com/problems/rotate-image/](https://leetcode.com/problems/rotate-image/)  
+- [X] Word Search - [https://leetcode.com/problems/word-search/](https://leetcode.com/problems/word-search/)
+
+---
+
+#### String
+
+- [X] Longest Substring Without Repeating Characters - [https://leetcode.com/problems/longest-substring-without-repeating-characters/](https://leetcode.com/problems/longest-substring-without-repeating-characters/)  
+- [X] Longest Repeating Character Replacement - [https://leetcode.com/problems/longest-repeating-character-replacement/](https://leetcode.com/problems/longest-repeating-character-replacement/)  
+- [X] Minimum Window Substring - [https://leetcode.com/problems/minimum-window-substring/](https://leetcode.com/problems/minimum-window-substring/)  
+- [X] Valid Anagram - [https://leetcode.com/problems/valid-anagram/](https://leetcode.com/problems/valid-anagram/)  
+- [X] Group Anagrams - [https://leetcode.com/problems/group-anagrams/](https://leetcode.com/problems/group-anagrams/)  
+- [X] Valid Parentheses - [https://leetcode.com/problems/valid-parentheses/](https://leetcode.com/problems/valid-parentheses/)  
+- [X] Valid Palindrome - [https://leetcode.com/problems/valid-palindrome/](https://leetcode.com/problems/valid-palindrome/)  
+- [X] Longest Palindromic Substring - [https://leetcode.com/problems/longest-palindromic-substring/](https://leetcode.com/problems/longest-palindromic-substring/)  
+- [X] Palindromic Substrings - [https://leetcode.com/problems/palindromic-substrings/](https://leetcode.com/problems/palindromic-substrings/)  
+- [X] Encode and Decode Strings (Leetcode Premium) - [https://leetcode.com/problems/encode-and-decode-strings/](https://leetcode.com/problems/encode-and-decode-strings/)
+
+---
+
+#### Tree
+
+- [X] Maximum Depth of Binary Tree - [https://leetcode.com/problems/maximum-depth-of-binary-tree/](https://leetcode.com/problems/maximum-depth-of-binary-tree/)  
+- [X] Same Tree - [https://leetcode.com/problems/same-tree/](https://leetcode.com/problems/same-tree/)  
+- [X] Invert/Flip Binary Tree - [https://leetcode.com/problems/invert-binary-tree/](https://leetcode.com/problems/invert-binary-tree/)  
+- [X] Binary Tree Maximum Path Sum - [https://leetcode.com/problems/binary-tree-maximum-path-sum/](https://leetcode.com/problems/binary-tree-maximum-path-sum/)  
+- [X] Binary Tree Level Order Traversal - [https://leetcode.com/problems/binary-tree-level-order-traversal/](https://leetcode.com/problems/binary-tree-level-order-traversal/)  
+- [X] Serialize and Deserialize Binary Tree - [https://leetcode.com/problems/serialize-and-deserialize-binary-tree/](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/)  
+- [X] Subtree of Another Tree - [https://leetcode.com/problems/subtree-of-another-tree/](https://leetcode.com/problems/subtree-of-another-tree/)  
+- [X] Construct Binary Tree from Preorder and Inorder Traversal - [https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/](https://leetcode.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)  
+- [X] Validate Binary Search Tree - [https://leetcode.com/problems/validate-binary-search-tree/](https://leetcode.com/problems/validate-binary-search-tree/)  
+- [X] Kth Smallest Element in a BST - [https://leetcode.com/problems/kth-smallest-element-in-a-bst/](https://leetcode.com/problems/kth-smallest-element-in-a-bst/)  
+- [X] Lowest Common Ancestor of BST - [https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/)  
+- [X] Implement Trie (Prefix Tree) - [https://leetcode.com/problems/implement-trie-prefix-tree/](https://leetcode.com/problems/implement-trie-prefix-tree/)  
+- [X] Add and Search Word - [https://leetcode.com/problems/add-and-search-word-data-structure-design/](https://leetcode.com/problems/add-and-search-word-data-structure-design/)  
+- [X] Word Search II - [https://leetcode.com/problems/word-search-ii/](https://leetcode.com/problems/word-search-ii/)
+
+---
+
+#### Heap
+
+- [X] Merge K Sorted Lists - [https://leetcode.com/problems/merge-k-sorted-lists/](https://leetcode.com/problems/merge-k-sorted-lists/)  
+- [X] Top K Frequent Elements - [https://leetcode.com/problems/top-k-frequent-elements/](https://leetcode.com/problems/top-k-frequent-elements/)  
+- [X] Find Median from Data Stream - [https://leetcode.com/problems/find-median-from-data-stream/](https://leetcode.com/problems/find-median-from-data-stream/)

add_two_numbers_2/README.md

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+# 2. Add Two Numbers
+
+https://leetcode.com/problems/add-two-numbers/
+
+# Description
+
+You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
+
+You may assume the two numbers do not contain any leading zero, except the number 0 itself.
+
+Example:
+```
+Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
+Output: 7 -> 0 -> 8
+Explanation: 342 + 465 = 807.
+```

add_two_numbers_2/solution.go

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+package add_two_numbers_2
+
+import (
+	"github.com/austingebauer/leetcode/structures"
+	"math/big"
+)
+
+func addTwoNumbers(l1 *structures.ListNode, l2 *structures.ListNode) *structures.ListNode {
+	num1 := depthFirstNum(l1)
+	num2 := depthFirstNum(l2)
+
+	var sum big.Int
+	sum.Add(num1, num2)
+
+	// single digit sum
+	if len(sum.String()) == 1 {
+		return &structures.ListNode{
+			Val:  int(sum.Int64()),
+			Next: nil,
+		}
+	}
+
+	var sumList *structures.ListNode
+	var current *structures.ListNode
+
+	for sum.String() != "0" {
+		var lastDigit big.Int
+		lastDigit.Mod(&sum, big.NewInt(10))
+
+		node := &structures.ListNode{
+			Val:  int(lastDigit.Int64()),
+			Next: nil,
+		}
+		if sumList == nil {
+			sumList = node
+		}
+		if current == nil {
+			current = node
+		} else {
+			current.Next = node
+			current = current.Next
+		}
+
+		sum.Div(&sum, big.NewInt(10))
+	}
+
+	return sumList
+}
+
+func depthFirstNum(l *structures.ListNode) *big.Int {
+	if l == nil {
+		return big.NewInt(0)
+	}
+
+	v := depthFirstNum(l.Next)
+	return v.Mul(v, big.NewInt(10)).Add(v, big.NewInt(int64(l.Val)))
+}
+
+func addTwoNumbers2(l1 *structures.ListNode, l2 *structures.ListNode) *structures.ListNode {
+	carry := 0
+	sumList := &structures.ListNode{
+		Val:  0,
+		Next: nil,
+	}
+	frontSumList := sumList
+
+	for l1 != nil || l2 != nil {
+		// calculate sum and carry values
+		l1Val := 0
+		l2Val := 0
+		if l1 != nil {
+			l1Val = l1.Val
+			l1 = l1.Next
+		}
+		if l2 != nil {
+			l2Val = l2.Val
+			l2 = l2.Next
+		}
+
+		sum := l1Val + l2Val + carry
+		carry = sum / 10
+		sumList.Val = sum % 10
+
+		// no more list to process, but carry is not 0
+		if l1 == nil && l2 == nil && carry > 0 {
+			sumList.Next = &structures.ListNode{
+				Val:  carry,
+				Next: nil,
+			}
+		}
+
+		// one or both lists still can be processed
+		if l1 != nil || l2 != nil {
+			sumList.Next = &structures.ListNode{
+				Val:  0,
+				Next: nil,
+			}
+			sumList = sumList.Next
+		}
+	}
+
+	return frontSumList
+}