From d35c23f5978885f91feecc24a56e3c7a549e667f Mon Sep 17 00:00:00 2001 From: HC-kang Date: Mon, 9 Sep 2024 08:45:32 +0900 Subject: [PATCH 1/5] Feat: 121. Best Time to Buy and Sell Stock --- best-time-to-buy-and-sell-stock/HC-kang.ts | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) create mode 100644 best-time-to-buy-and-sell-stock/HC-kang.ts diff --git a/best-time-to-buy-and-sell-stock/HC-kang.ts b/best-time-to-buy-and-sell-stock/HC-kang.ts new file mode 100644 index 00000000..8da2beec --- /dev/null +++ b/best-time-to-buy-and-sell-stock/HC-kang.ts @@ -0,0 +1,19 @@ +// https://leetcode.com/problems/best-time-to-buy-and-sell-stock/ +// T.C: O(N) +// S.C: O(1) +function maxProfit(prices: number[]): number { + let min = prices[0]; + let max = prices[0]; + let candidate = prices[0]; + + for (let i = 1; i < prices.length; i++) { + if (prices[i] < candidate) { + candidate = prices[i]; + } else if (prices[i] - candidate > max - min) { + min = candidate; + max = prices[i]; + } + } + + return max - min; +} From 91f32d6ac145d81b40a0b1881d111e7f4901b8a8 Mon Sep 17 00:00:00 2001 From: HC-kang Date: Tue, 10 Sep 2024 08:28:46 +0900 Subject: [PATCH 2/5] Feat: 49. Group Anagrams --- group-anagrams/HC-kang.ts | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) create mode 100644 group-anagrams/HC-kang.ts diff --git a/group-anagrams/HC-kang.ts b/group-anagrams/HC-kang.ts new file mode 100644 index 00000000..82861e6d --- /dev/null +++ b/group-anagrams/HC-kang.ts @@ -0,0 +1,19 @@ +/** + * https://leetcode.com/problems/group-anagrams/description + * T.C: O(n * m * log(m)), n = strs.length, m = max(strs[i].length) + * S.C: O(n * m) + */ +function groupAnagrams(strs: string[]): string[][] { + const map = new Map(); + + for (const str of strs) { // O(n) + const sorted = str.split('').sort().join(''); // O(m * log(m)) + + if (map.has(sorted)) + map.get(sorted)!.push(str); + else + map.set(sorted, [str]); + } + + return Array.from(map.values()); +} From c30493747c4e06b7188703845a1e1b53e3beffd6 Mon Sep 17 00:00:00 2001 From: HC-kang Date: Tue, 10 Sep 2024 09:04:40 +0900 Subject: [PATCH 3/5] Feat: 15. 3Sum --- 3sum/HC-kang.ts | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) create mode 100644 3sum/HC-kang.ts diff --git a/3sum/HC-kang.ts b/3sum/HC-kang.ts new file mode 100644 index 00000000..7be7e187 --- /dev/null +++ b/3sum/HC-kang.ts @@ -0,0 +1,36 @@ +/** + * https://leetcode.com/problems/3sum/description + * T.C: O(n^2) + * S.C: O(1) + */ +function threeSum(nums: number[]): number[][] { + nums.sort((a, b) => a - b); + + const result: number[][] = []; + + for (let i = 0; i < nums.length - 2; i++) { // O(n) + if (i > 0 && nums[i] == nums[i - 1]) continue; + + let left = i + 1; + let right = nums.length - 1; + + while (left < right) { // O(n) + const sum = nums[i] + nums[left] + nums[right]; + if (sum == 0) { + result.push([nums[i], nums[left], nums[right]]); + + while (left < right && nums[left] == nums[left + 1]) left++; + while (left < right && nums[right] == nums[right - 1]) right--; + + left++; + right--; + } else if (sum < 0) { + left++; + } else { + right--; + } + } + } + + return result; +} From f89c4c632361c77254e89523747a3c1c8faca1ae Mon Sep 17 00:00:00 2001 From: HC-kang Date: Wed, 11 Sep 2024 08:55:31 +0900 Subject: [PATCH 4/5] Feat: 208. Implement Trie (Prefix Tree) --- implement-trie-prefix-tree/HC-kang.ts | 47 +++++++++++++++++++++++++++ 1 file changed, 47 insertions(+) create mode 100644 implement-trie-prefix-tree/HC-kang.ts diff --git a/implement-trie-prefix-tree/HC-kang.ts b/implement-trie-prefix-tree/HC-kang.ts new file mode 100644 index 00000000..e7b1908f --- /dev/null +++ b/implement-trie-prefix-tree/HC-kang.ts @@ -0,0 +1,47 @@ +/** + * https://leetcode.com/problems/implement-trie-prefix-tree + */ +class Trie { + constructor(private root: Record = {}) {} + + insert(word: string): void { + let node = this.root; + for (const char of word) { + if (!node[char]) { + node[char] = {}; + } + node = node[char]; + } + node.isEnd = true; + } + + search(word: string): boolean { + let node = this.root; + for (const char of word) { + if (!node[char]) { + return false; + } + node = node[char]; + } + return !!node.isEnd; + } + + startsWith(prefix: string): boolean { + let node = this.root; + for (const char of prefix) { + if (!node[char]) { + return false; + } + node = node[char]; + } + return true; + } +} + +/** + * Your Trie object will be instantiated and called as such: + * var obj = new Trie() + * obj.insert(word) + * var param_2 = obj.search(word) + * var param_3 = obj.startsWith(prefix) + */ From 5cb3615da91b5c93206752eb286d62941639ceab Mon Sep 17 00:00:00 2001 From: HC-kang Date: Wed, 11 Sep 2024 21:26:21 +0900 Subject: [PATCH 5/5] Feat: 139. Word Break --- word-break/HC-kang.ts | 23 +++++++++++++++++++++++ 1 file changed, 23 insertions(+) create mode 100644 word-break/HC-kang.ts diff --git a/word-break/HC-kang.ts b/word-break/HC-kang.ts new file mode 100644 index 00000000..4bc3318c --- /dev/null +++ b/word-break/HC-kang.ts @@ -0,0 +1,23 @@ +/** + * https://leetcode.com/problems/word-break + * T.C. O(s^2) + * S.C. O(s + w) + */ +function wordBreak(s: string, wordDict: string[]): boolean { + const wordSet = new Set(wordDict); + + const dp = new Array(s.length + 1).fill(false); + dp[0] = true; + + for (let i = 1; i <= s.length; i++) { + for (let j = 0; j < i; j++) { + if (!dp[j]) continue; + if (j-i > 20) break; + if (wordSet.has(s.slice(j, i))) { + dp[i] = true; + break; + } + } + } + return dp[s.length]; +}