Merge pull request #2497 from tedkimdev/tedkimdev/week5

[tedkimdev] WEEK 05 Solutions

Author: tedkimdev

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

@@ -0,0 +1,20 @@
+// TC: O(n)
+// SC: O(1)
+func maxProfit(prices []int) int {
+	l, r := 0, 1
+	max := 0
+
+	for r < len(prices) {
+		if prices[l] < prices[r] {
+			profit := prices[r] - prices[l]
+			if profit > max {
+				max = profit
+			}
+		} else {
+			l = r
+		}
+		r++
+	}
+
+	return max
+}

encode-and-decode-strings/tedkimdev.go

@@ -0,0 +1,32 @@
+type Solution struct{}
+
+// TC: O(m)
+// SC: O(m + n)
+func (s *Solution) Encode(strs []string) string {
+	encoded := ""
+	for _, str := range strs {
+		encoded += fmt.Sprintf("%d|%s", len(str), str)
+	}
+
+	return encoded
+}
+
+// TC: O(m)
+// SC: O(m + n)
+func (s *Solution) Decode(encoded string) []string {
+	decoded := make([]string, 0)
+
+	i := 0
+	for i < len(encoded) {
+		j := i
+		for encoded[j] != '|' {
+			j++
+		}
+		length, _ := strconv.Atoi(encoded[i:j])
+		i = j + 1
+		decoded = append(decoded, encoded[i:i+length])
+		i += length
+	}
+
+	return decoded
+}

group-anagrams/tedkimdev.go

@@ -0,0 +1,19 @@
+// TC: O(m * n)
+// SC: O(m * n)
+func groupAnagrams(strs []string) [][]string {
+	groups := map[[26]int][]string{}
+
+	for _, s := range strs {
+		var count [26]int
+		for _, c := range s {
+			count[c-'a']++
+		}
+		groups[count] = append(groups[count], s)
+	}
+
+	result := [][]string{}
+	for _, group := range groups {
+		result = append(result, group)
+	}
+	return result
+}

implement-trie-prefix-tree/tedkimdev.go

@@ -0,0 +1,52 @@
+// TC: O(n)
+// SC: O(t) - Where n is the length of the string and t is the total number of TrieNodes created in the Trie.
+type PrefixTree struct {
+	children map[rune]*PrefixTree
+	isWord   bool
+}
+
+func Constructor() PrefixTree {
+	return PrefixTree{
+		children: map[rune]*PrefixTree{},
+		isWord:   false,
+	}
+}
+
+func (this *PrefixTree) Insert(word string) {
+	cur := this
+	for _, c := range word {
+		if _, ok := cur.children[c]; !ok {
+			child := Constructor()
+			cur.children[c] = &child
+			cur = cur.children[c]
+		} else {
+			cur = cur.children[c]
+		}
+	}
+	cur.isWord = true
+}
+
+func (this *PrefixTree) Search(word string) bool {
+	cur := this
+	for _, c := range word {
+		if _, ok := cur.children[c]; ok {
+			cur = cur.children[c]
+		} else {
+			return false
+		}
+	}
+	return cur.isWord
+}
+
+func (this *PrefixTree) StartsWith(prefix string) bool {
+	cur := this
+	for _, c := range prefix {
+		if _, ok := cur.children[c]; ok {
+			cur = cur.children[c]
+		} else {
+			return false
+		}
+	}
+
+	return cur != nil
+}

word-break/tedkimdev.go

@@ -0,0 +1,67 @@
+// TC: O((n * t) + (m * t))
+// SC: O(n + (m * t))
+func wordBreak(s string, wordDict []string) bool {
+	trie := NewTrieNode()
+	maxLength := 0
+	for _, word := range wordDict {
+		trie.Insert(word)
+		if len(word) > maxLength {
+			maxLength = len(word)
+		}
+	}
+
+	dp := make([]bool, len(s)+1)
+	dp[len(s)] = true
+
+	for i := len(s) - 1; i >= 0; i-- {
+		node := trie
+		for j := i; j < len(s) && j < i+maxLength; j++ {
+			c := s[j]
+			if _, ok := node.children[rune(c)]; !ok {
+				break
+			}
+			node = node.children[rune(c)]
+
+			if node.isWord && dp[j+1] {
+				dp[i] = true
+				break
+			}
+		}
+	}
+
+	return dp[0]
+}
+
+type TrieNode struct {
+	children map[rune]*TrieNode
+	isWord   bool
+}
+
+func NewTrieNode() *TrieNode {
+	return &TrieNode{children: make(map[rune]*TrieNode)}
+}
+
+func (t *TrieNode) Insert(word string) {
+	node := t
+	for _, char := range word {
+		if _, ok := node.children[char]; !ok {
+			node.children[char] = NewTrieNode()
+		}
+		node = node.children[char]
+	}
+	node.isWord = true
+}
+
+// func (t *TrieNode) Search(s string, i, j int) bool {
+//     node := t
+//     for idx := i; idx <= j; idx++ {
+//         char := rune(s[idx])
+//         if _, ok := node.children[char]; !ok {
+//             return false
+//         }
+//         node = node.children[char]
+//     }
+//     return node.isWord
+// }
+
+