[강희찬] WEEK 5 Solution

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;
+}

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;
+}

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<string, string[]>();
+
+  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());
+}

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<string, any> = {}) {}
+
+  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)
+ */

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];
+}