[jinho] Week 2

3sum/neverlish.go

@@ -0,0 +1,79 @@
+// 시간복잡도: O(n^2)
+// 공간복잡도: O(n)
+
+package main
+
+import (
+	"sort"
+	"testing"
+)
+
+func TestThreeSum(t *testing.T) {
+	test1 := []int{-1, 0, 1, 2, -1, -4}
+	result1 := threeSum(test1)
+
+	for _, comp := range result1 {
+		for _, num := range comp {
+			t.Logf("%d ", num)
+		}
+	}
+
+	println("YO")
+
+	if len(result1) != 2 {
+		t.Errorf("Expected 2, got %d", len(result1))
+	}
+}
+
+func twoSum(nums []int, target int) [][]int {
+	result := [][]int{}
+	seen := map[int]int{}
+	for i, num := range nums {
+		complement := target - num
+		if _, ok := seen[complement]; ok {
+			result = append(result, []int{seen[complement], i})
+		}
+		seen[num] = i
+	}
+
+	return result
+}
+
+func threeSum(nums []int) [][]int {
+	result := map[int]map[int]map[int]bool{}
+
+	for i, num := range nums[:len(nums)-2] {
+		if (i > 0 && num == nums[i-1]) {
+			continue
+		}
+		for _, comp := range twoSum(nums[i+1:], 0-num) {
+			comps := []int{num, nums[comp[0]+i+1], nums[comp[1]+i+1]}
+			sort.Ints(comps)
+			comp1 := comps[0]
+			comp2 := comps[1]
+			comp3 := comps[2]
+			if _, ok := result[comp1]; !ok {
+				result[comp1] = map[int]map[int]bool{}
+			}
+			if _, ok := result[comp1][comp2]; !ok {
+				result[comp1][comp2] = map[int]bool{}
+			}
+			result[comp1][comp2][comp3] = true
+		}
+	}
+
+
+
+	answers := [][]int{}
+	for key1 := range result {
+
+		for key2 := range result[key1] {
+			for key3 := range result[key1][key2] {
+				comp := []int{key1, key2, key3}
+				answers = append(answers, comp)
+			}
+		}
+	}
+
+	return answers
+}

climbing-stairs/neverlish.go

@@ -0,0 +1,43 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+package main
+
+import (
+	"testing"
+)
+
+func Test(t *testing.T) {
+	result1 := climbStairs(2)
+
+	if result1 != 2 {
+		t.Fatal("failed test1")
+	}
+
+	result2 := climbStairs(3)
+
+	if result2 != 3 {
+		t.Fatal("failed test2")
+	}
+}
+
+func climbStairs(n int) int {
+
+	if n == 1 {
+		return 1
+	}
+
+	if n == 2 {
+		return 2
+	}
+	dp := make([]int, n+1)
+
+	dp[1] = 1
+	dp[2] = 2
+
+	for i := 3; i <= n; i++ {
+		dp[i] = dp[i-1] + dp[i-2]
+	}
+
+	return dp[n]
+}

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

@@ -0,0 +1,48 @@
+package main
+
+import "testing"
+
+func TestBuildTree(t *testing.T) {
+	preorder := []int{3,9,20,15,7}
+	inorder := []int{9,3,15,20,7}
+
+	result := buildTree(preorder, inorder)
+	println(result.Val)
+	println(result.Left.Val)
+	println(result.Right.Val)
+	println(result.Right.Left.Val)
+	println(result.Right.Right.Val)
+}
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func findIndex(target int, values []int) int {
+	for i, v := range values {
+		if v == target {
+			return i
+		}
+	}
+	return -1
+}
+
+func buildTree(preorder []int, inorder []int) *TreeNode {
+	if len(inorder) == 0 {
+		return nil
+	}
+	Val := preorder[0]
+
+	midIndex := findIndex(Val, inorder)
+
+	Left := buildTree(preorder[1:midIndex+1], inorder[:midIndex])
+	Right := buildTree(preorder[midIndex+1:], inorder[midIndex+1:])
+
+	return &TreeNode{
+		Val,
+		Left,
+		Right,
+	}
+}

decode-ways/neverlish.go

@@ -0,0 +1,59 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+package main
+
+import (
+	"testing"
+)
+
+func TestNumDecodings(t *testing.T) {
+	test1 := "12"
+	result1 := numDecodings(test1)
+
+	if result1 != 2 {
+		t.Errorf("Expected 2, got %d", result1)
+	}
+
+	test2 := "226"
+	result2 := numDecodings(test2)
+
+	if result2 != 3 {
+		t.Errorf("Expected 3, got %d", result2)
+	}
+
+	test3 := "0"
+	result3 := numDecodings(test3)
+
+	if result3 != 0 {
+		t.Errorf("Expected 0, got %d", result3)
+	}
+
+	test4 := "06"
+	result4 := numDecodings(test4)
+
+	if result4 != 0 {
+		t.Errorf("Expected 0, got %d", result4)
+	}
+}
+
+func numDecodings(s string) int {
+	dp := make([]int, len(s)+1)
+
+	dp[0] = 1
+
+	for i := 1; i <= len(s); i++ {
+		curBefore1 := s[i-1]
+		if curBefore1 != '0' {
+			dp[i] += dp[i-1]
+		}
+		if i > 1 {
+			curBefore2 := s[i-2]
+			if curBefore2 != '0' && (curBefore2-'0')*10+(curBefore1-'0') <= 26 {
+				dp[i] += dp[i-2]
+			}
+		}
+	}
+
+	return dp[len(s)]
+}

valid-anagram/neverlish.go

@@ -0,0 +1,48 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+package main
+
+import (
+	"testing"
+)
+
+func Test(t *testing.T) {
+	result1 := isAnagram("anagram", "nagaram")
+
+	if !result1 {
+		t.Fatal("failed test1")
+	}
+
+	result2 := isAnagram("rat", "car")
+
+	if result2 {
+		t.Fatal("failed test2")
+	}
+}
+
+func isAnagram(s string, t string) bool {
+	if len(s) != len(t) {
+		return false
+	}
+
+	sMap := make(map[rune]int)
+
+	for _, c := range s {
+		sMap[c]++
+	}
+
+	for _, c := range t {
+		if _, ok := sMap[c]; !ok {
+			return false
+		}
+
+		sMap[c]--
+
+		if sMap[c] == 0 {
+			delete(sMap, c)
+		}
+	}
+
+	return len(sMap) == 0
+}