[jinho] week5 (#878)

Author: neverlish

best-time-to-buy-and-sell-stock/neverlish.go

@@ -0,0 +1,34 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(1)
+
+package main
+
+import "testing"
+
+func TestMaxProfit(t *testing.T) {
+	prices := []int{7, 1, 5, 3, 6, 4}
+	if maxProfit(prices) != 5 {
+		t.Error("Test case 0 failed")
+	}
+
+	prices = []int{7, 6, 4, 3, 1}
+	if maxProfit(prices) != 0 {
+		t.Error("Test case 1 failed")
+	}
+}
+
+func maxProfit(prices []int) int {
+	minPrice := prices[0]
+	result := 0
+
+	for _, price := range prices {
+		profit := price - minPrice
+		if profit > result {
+			result = profit
+		}
+		if price < minPrice {
+			minPrice = price
+		}
+	}
+	return result
+}

encode-and-decode-strings/neverlish.go

@@ -0,0 +1,48 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+	"testing"
+)
+
+func TestEncodeAndDecode(t *testing.T) {
+	strs := []string{"abc", "def", "ghi"}
+	encoded := encode(strs)
+	decoded := decode(encoded)
+	if len(strs) != len(decoded) {
+		t.Errorf("Expected %v but got %v", strs, decoded)
+	}
+	for i := 0; i < len(strs); i++ {
+		if strs[i] != decoded[i] {
+			t.Errorf("Expected %v but got %v", strs, decoded)
+		}
+	}
+}
+
+func encode(strs []string) string {
+	var buffer bytes.Buffer
+	for _, str := range strs {
+		buffer.WriteString(fmt.Sprintf("%d~", len(str)))
+		buffer.WriteString(str)
+	}
+	return buffer.String()
+}
+
+func decode(str string) []string {
+	var result []string
+	for i := 0; i < len(str); {
+		j := i
+		for str[j] != '~' {
+			j++
+		}
+		length, _ := strconv.Atoi(str[i:j])
+		result = append(result, str[j+1:j+1+length])
+		i = j + 1 + length
+	}
+	return result
+}

group-anagrams/neverlish.go

@@ -0,0 +1,49 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+package main
+
+import "testing"
+
+func TestGroupAnagrams(t *testing.T) {
+	strs := []string{"eat", "tea", "tan", "ate", "nat", "bat"}
+	result := groupAnagrams(strs)
+
+	if len(result) != 3 {
+		t.Error("Test case 0 failed")
+	}
+
+	if len(result[0]) != 3 {
+		t.Error("Test case 1 failed")
+	}
+
+	if len(result[1]) != 3 {
+		t.Error("Test case 2 failed")
+	}
+
+	if len(result[2]) != 1 {
+		t.Error("Test case 3 failed")
+	}
+}
+
+func groupAnagrams(strs []string) [][]string {
+	result := make([][]string, 0)
+
+	m := make(map[[26]int]int)
+
+	for _, str := range strs {
+		key := [26]int{}
+		for _, c := range str {
+			key[c-'a']++
+		}
+
+		if idx, ok := m[key]; ok {
+			result[idx] = append(result[idx], str)
+		} else {
+			m[key] = len(result)
+			result = append(result, []string{str})
+		}
+	}
+
+	return result
+}

implement-trie-prefix-tree/neverlish.go

@@ -0,0 +1,54 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+package main
+
+type Trie struct {
+	children map[byte]*Trie
+	isEnd    bool
+}
+
+func Constructor() Trie {
+	return Trie{children: make(map[byte]*Trie)}
+}
+
+func (this *Trie) Insert(word string) {
+	for i := 0; i < len(word); i++ {
+		if _, ok := this.children[word[i]]; !ok {
+			this.children[word[i]] = &Trie{children: make(map[byte]*Trie)}
+		}
+		this = this.children[word[i]]
+	}
+	this.isEnd = true
+}
+
+func (this *Trie) Search(word string) bool {
+	for i := 0; i < len(word); i++ {
+		if _, ok := this.children[word[i]]; !ok {
+			return false
+		}
+		this = this.children[word[i]]
+	}
+	if this.isEnd {
+		return true
+	}
+	return false
+}
+
+func (this *Trie) StartsWith(prefix string) bool {
+	for i := 0; i < len(prefix); i++ {
+		if _, ok := this.children[prefix[i]]; !ok {
+			return false
+		}
+		this = this.children[prefix[i]]
+	}
+	return true
+}
+
+/**
+ * Your Trie object will be instantiated and called as such:
+ * obj := Constructor();
+ * obj.Insert(word);
+ * param_2 := obj.Search(word);
+ * param_3 := obj.StartsWith(prefix);
+ */

word-break/neverlish.go

@@ -0,0 +1,46 @@
+// 시간복잡도: O(n^2)
+// 공간복잡도: O(n)
+
+package main
+
+import "testing"
+
+func TestWordBreak(t *testing.T) {
+
+	result1 := wordBreak("leetcode", []string{"leet", "code"})
+	if result1 != true {
+		t.Error("Test case 0 failed")
+	}
+
+	result2 := wordBreak("applepenapple", []string{"apple", "pen"})
+	if result2 != true {
+		t.Error("Test case 1 failed")
+	}
+
+	result3 := wordBreak("catsandog", []string{"cats", "dog", "sand", "and", "cat"})
+	if result3 != false {
+		t.Error("Test case 2 failed")
+	}
+}
+
+func wordBreak(s string, wordDict []string) bool {
+	wordMap := make(map[string]bool)
+
+	for _, word := range wordDict {
+		wordMap[word] = true
+	}
+
+	dp := make([]bool, len(s)+1)
+	dp[0] = true
+	for i := 1; i <= len(s); i++ {
+		for j := 0; j < i; j++ {
+			word := s[j:i]
+			if dp[j] && wordMap[word] {
+				dp[i] = true
+				break
+			}
+		}
+	}
+
+	return dp[len(s)]
+}