Up to unique paths

.gitignore

@@ -0,0 +1 @@
+.vscode/

binary-tree-maximum-path-sum.go

@@ -0,0 +1,48 @@
+package main
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func max2(a, b int) int {
+	if a > b {
+		return a
+	}
+
+	return b
+}
+
+func max3(a, b, c int) int {
+	return max2(a, max2(b, c))
+}
+
+func traverse(root *TreeNode, maxSum *int) int {
+	if root == nil {
+		return 0
+	}
+
+	lPathMaxSum := traverse(root.Left, maxSum)
+	rPathMaxSum := traverse(root.Right, maxSum)
+	rootPathMaxSum := max3(root.Val, root.Val+lPathMaxSum, root.Val+rPathMaxSum)
+
+	*maxSum = max3(*maxSum, root.Val+lPathMaxSum+rPathMaxSum, rootPathMaxSum)
+
+	return rootPathMaxSum
+}
+
+func maxPathSum(root *TreeNode) int {
+	if root == nil {
+		return 0
+	}
+
+	maxSum := root.Val
+	traverse(root, &maxSum)
+
+	return maxSum
+}
+
+func main() {
+
+}

combination-sum-2.go

@@ -0,0 +1,62 @@
+package main
+
+import (
+	"fmt"
+	"sort"
+)
+
+type Ints []int
+
+func (ints Ints) Len() int {
+	return len(ints)
+}
+
+func (ints Ints) Less(i, j int) bool {
+	return ints[i] < ints[j]
+}
+
+func (ints Ints) Swap(i, j int) {
+	ints[i], ints[j] = ints[j], ints[i]
+}
+
+func findCombinations(candidates []int, target int, selectedCandidates []int, results [][]int) [][]int {
+	if target < 0 {
+		return results
+	}
+
+	if target == 0 {
+		sel := make([]int, len(selectedCandidates))
+		copy(sel, selectedCandidates)
+		results = append(results, sel)
+
+		return results
+	}
+
+	for i := 0; i < len(candidates); i++ {
+		if i > 0 && candidates[i] == candidates[i-1] {
+			continue
+		}
+
+		selectedCandidates = append(selectedCandidates, candidates[i])
+		results = findCombinations(candidates[i+1:], target-candidates[i], selectedCandidates, results)
+		selectedCandidates = selectedCandidates[:len(selectedCandidates)-1]
+	}
+
+	return results
+}
+
+func combinationSum2(candidates []int, target int) [][]int {
+	sort.Sort(Ints(candidates))
+
+	return findCombinations(candidates, target, []int{}, [][]int{})
+}
+
+func tests() {
+	fmt.Printf("%v\n", combinationSum2([]int{10, 1, 2, 7, 6, 1, 5}, 8))
+	fmt.Printf("%v\n", combinationSum2([]int{2, 5, 2, 1, 2}, 5))
+	fmt.Printf("%v\n", combinationSum2([]int{1, 1, 2, 2}, 5))
+}
+
+func main() {
+	tests()
+}

construct-binary-tree-from-preorder-and-inorder-traversal.go

@@ -0,0 +1,85 @@
+package main
+
+import "fmt"
+
+/**
+ * Definition for a binary tree node.
+ * type TreeNode struct {
+ *     Val int
+ *     Left *TreeNode
+ *     Right *TreeNode
+ * }
+ */
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func getSubTree(preorder []int, preorderStart, preorderEnd int, inorder []int, inorderStart, inorderEnd int, preorderOffsetLUT, inorderOffsetLUT map[int]int) *TreeNode {
+	if len(preorder) == 0 || len(inorder) == 0 || preorderStart > preorderEnd || inorderStart > inorderEnd {
+		return nil
+	}
+
+	root := preorder[preorderStart]
+	rootInorderOffset := inorderOffsetLUT[root]
+	lSubTreeLen := rootInorderOffset - inorderStart
+
+	if lSubTreeLen < 0 {
+		fmt.Printf("****ERROR******\n")
+		fmt.Printf("root: %d; preorderStart: %d; inorderStart: %d; rootInorderOffset: %d; lSubTreeLen: %d\n",
+			root, preorderStart, inorderStart, rootInorderOffset, lSubTreeLen)
+
+		return nil
+	}
+
+	// fmt.Printf("getting lSubTree\n")
+	lSubTree := getSubTree(preorder, preorderStart+1, preorderStart+1+lSubTreeLen-1,
+		inorder, inorderStart, inorderStart+lSubTreeLen-1, preorderOffsetLUT, inorderOffsetLUT)
+
+	// fmt.Printf("getting rSubTree\n")
+	rSubTree := getSubTree(preorder, preorderStart+lSubTreeLen+1, preorderEnd,
+		inorder, rootInorderOffset+1, inorderEnd, preorderOffsetLUT, inorderOffsetLUT)
+
+	return &TreeNode{Val: root, Left: lSubTree, Right: rSubTree}
+}
+
+func inorderTraversal(root *TreeNode) {
+	if root == nil {
+		return
+	}
+
+	inorderTraversal(root.Left)
+	fmt.Printf("%d ", root.Val)
+	inorderTraversal(root.Right)
+}
+
+func buildTree(preorder []int, inorder []int) *TreeNode {
+	preorderOffsetLUT := make(map[int]int)
+	inorderOffsetLUT := make(map[int]int)
+
+	for i := 0; i < len(preorder); i++ {
+		preorderOffsetLUT[preorder[i]] = i
+		inorderOffsetLUT[inorder[i]] = i
+	}
+
+	return getSubTree(preorder, 0, len(preorder)-1, inorder, 0, len(inorder)-1, preorderOffsetLUT, inorderOffsetLUT)
+}
+
+func test1() {
+	// preorder := []int{3, 9, 20, 15, 7}
+	// inorder := []int{9, 3, 15, 20, 7}
+	preorder := []int{5, 1, 9}
+	inorder := []int{1, 5, 9}
+	// preorder := []int{1, 5}
+	// inorder := []int{1, 5}
+
+	tree := buildTree(preorder, inorder)
+
+	inorderTraversal(tree)
+}
+
+func main() {
+	test1()
+}

course-schedule-ii.go

@@ -0,0 +1,190 @@
+package main
+
+import "fmt"
+
+type intSet struct {
+	size     int
+	elements map[int]struct{}
+}
+
+func NewIntSet() intSet {
+	return intSet{size: 0, elements: make(map[int]struct{})}
+}
+
+func (s *intSet) Add(elem int) {
+	if _, exists := s.elements[elem]; !exists {
+		s.elements[elem] = struct{}{}
+		s.size++
+	}
+
+	return
+}
+
+func (s *intSet) Remove(elem int) {
+	if _, exists := s.elements[elem]; exists {
+		delete(s.elements, elem)
+		s.size--
+	}
+
+	return
+}
+
+func (s *intSet) Contains(elem int) bool {
+	_, exists := s.elements[elem]
+
+	return exists
+}
+
+func (s *intSet) GetAnyElement() (int, error) {
+	if len(s.elements) == 0 {
+		return 0, fmt.Errorf("set is empty")
+	}
+
+	var elem int
+	for k, _ := range s.elements {
+		elem = k
+
+		break
+	}
+
+	return elem, nil
+}
+
+// Return true if cycle exists.
+func checkCycleFrom(start int, adjs [][]int, whiteSet, graySet, blackSet intSet) bool {
+	if blackSet.Contains(start) {
+		return false
+	}
+
+	if graySet.Contains(start) {
+		return true
+	}
+
+	if whiteSet.Contains(start) {
+		whiteSet.Remove(start)
+		graySet.Add(start)
+	}
+
+	// Explore all adjacencies
+	for i := 0; i < len(adjs[start]); i++ {
+		cycleExists := checkCycleFrom(adjs[start][i], adjs, whiteSet, graySet, blackSet)
+
+		if cycleExists {
+			return true
+		}
+	}
+
+	graySet.Remove(start)
+	blackSet.Add(start)
+
+	return false
+}
+
+func checkCycle(adjs [][]int) bool {
+	whiteSet, graySet, blackSet := NewIntSet(), NewIntSet(), NewIntSet()
+
+	for i := 0; i < len(adjs); i++ {
+		whiteSet.Add(i)
+	}
+
+	for {
+		elem, err := whiteSet.GetAnyElement()
+
+		if err != nil {
+			break
+		}
+
+		if checkCycleFrom(elem, adjs, whiteSet, graySet, blackSet) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func topologicalTraversal(start int, adjs [][]int, visited map[int]struct{}, traversal []int) []int {
+	if _, exists := visited[start]; exists {
+		return traversal
+	}
+
+	for _, to := range adjs[start] {
+		traversal = topologicalTraversal(to, adjs, visited, traversal)
+	}
+
+	visited[start] = struct{}{}
+	traversal = append(traversal, start)
+
+	return traversal
+}
+
+func findOrder(numCourses int, prerequisites [][]int) []int {
+	adjs := make([][]int, numCourses)
+
+	for i, _ := range adjs {
+		adjs[i] = []int{}
+	}
+
+	visited := make(map[int]struct{})
+	leafCheck := make([]bool, numCourses)
+
+	for i, _ := range leafCheck {
+		leafCheck[i] = true
+	}
+
+	for _, pair := range prerequisites {
+		from, to := pair[0], pair[1]
+
+		adjs[from] = append(adjs[from], to)
+
+		leafCheck[to] = false
+	}
+
+	if checkCycle(adjs) {
+		return []int{}
+	}
+
+	order := []int{}
+
+	for i := 0; i < numCourses; i++ {
+		if leafCheck[i] {
+			// leaf course - this is a course that no other course depends on
+			order = topologicalTraversal(i, adjs, visited, order)
+		}
+	}
+
+	for i := 0; i < numCourses; i++ {
+		if _, exists := visited[i]; !exists {
+			return []int{}
+		}
+	}
+
+	return order
+}
+
+type testcase struct {
+	numCourses int
+	preReqs    [][]int
+}
+
+func tests() {
+	testcases := []testcase{
+		testcase{numCourses: 2, preReqs: [][]int{[]int{1, 0}}},
+		testcase{numCourses: 4, preReqs: [][]int{[]int{1, 0}, []int{2, 0}, []int{3, 1}, []int{3, 2}}},
+		testcase{numCourses: 3, preReqs: [][]int{[]int{0, 2}, []int{1, 2}, []int{2, 0}}},
+	}
+
+	for i, tc := range testcases {
+		order := findOrder(tc.numCourses, tc.preReqs)
+
+		fmt.Printf("Test case: %d; order: %v\n", i, order)
+	}
+}
+
+func main() {
+	// tests()
+	s1 := NewIntSet()
+
+	s1.Add(4)
+
+	fmt.Printf("s1.size = %d\n", s1.size)
+}