[hoyeongkwak] Week 05 Solutions

best-time-to-buy-and-sell-stock/hoyeongkwak.ts

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+/* 
+    time complexity : O(n)
+    space complexity : O(1)
+*/
+function maxProfit(prices: number[]): number {
+    let left = 0
+    let right = 0
+    let maxProfit = 0
+
+    while (right < prices.length) {
+        const curProfit = prices[right] - prices[left]
+        if (prices[left] < prices[right]) {
+            maxProfit = Math.max(curProfit, maxProfit)
+        } else {
+            left = right
+        }
+        right += 1
+    }
+    return maxProfit
+};

group-anagrams/hoyeongkwak.ts

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+/* 
+    time complexity : O(n * mlogm)
+    space complexity : O(n * m)
+*/
+function groupAnagrams(strs: string[]): string[][] {
+    const strMap = new Map<string, string[]>()
+    for (let i = 0; i < strs.length; i++) {
+        const sortedStr = strs[i].split('').sort().join('')
+        if (!strMap.has(sortedStr)) {
+            strMap.set(sortedStr, [strs[i]])
+        } else {
+            const prevArr = strMap.get(sortedStr)
+            prevArr.push(strs[i])
+            strMap.set(sortedStr, prevArr)
+        }
+    }
+    return Array.from(strMap.values())
+};

implement-trie-prefix-tree/hoyeongkwak.ts

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+/*
+    time complexity : O(n)
+    space complexity : O(n)
+*/
+class TriedNode {
+    children: Map<string, TriedNode>
+    isEnd: boolean
+    constructor(){
+        this.children = new Map()
+        this.isEnd = false
+    }
+}
+
+class Trie {
+    root: TriedNode
+
+    constructor() {
+        this.root = new TriedNode()
+    }
+
+    insert(word: string): void {
+        let node = this.root
+        for (const char of word) {
+            if (!node.children.has(char)) {
+                node.children.set(char, new TriedNode())
+            }
+            node = node.children.get(char)
+        }
+        node.isEnd = true
+    }
+
+    search(word: string): boolean {
+        let node = this.root
+        for (const char of word) {
+            if (!node.children.has(char)) {
+                return false
+            }
+            node = node.children.get(char)
+        }
+        return node.isEnd
+    }
+
+    startsWith(prefix: string): boolean {
+        let node = this.root
+        for (const char of prefix) {
+            if (!node.children.has(char)) {
+
+                return false
+            }
+            node = node.children.get(char)
+        }
+        return true
+    }
+}

word-break/hoyeongkwak.ts

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+/* 
+    time complexity : O(n^2k)
+    space complexity : O(n + m)
+*/
+
+function wordBreak(s: string, wordDict: string[]): boolean {
+   const dp: boolean[] = new Array(s.length + 1).fill(false)
+
+   dp[0] = true
+
+   const wordSet = new Set(wordDict)
+   for (let i = 1; i <= s.length; i++) {
+    for (let j = 0; j < i; j++) {
+        if (dp[j] && wordSet.has(s.substring(j, i))) {
+            dp[i] = true
+            break
+        }
+    }
+   }
+   return dp[s.length]
+};