Merge pull request #2397 from DaleStudy/jiji-hoon96/week2

[jiji-hoon96] WEEK 02 solutions

Author: jiji-hoon96

3sum/jiji-hoon96.ts

@@ -0,0 +1,69 @@
+// time limit 실패
+
+// function threeSum(nums: number[]): number[][] {
+// 	const result: number[][] = [];
+// 	for (let i = 0; i < nums.length; i++) {
+// 		for (let j = 1; j < nums.length; j++) {
+// 			for (let k = 2; k < nums.length; k++) {
+// 				if (
+// 					i !== j &&
+// 					j !== k &&
+// 					i !== k &&
+// 					nums[i] + nums[j] + nums[k] === 0
+// 				) {
+// 					const hasArray = result.some(
+// 						(item) =>
+// 							JSON.stringify([...item].sort((a, b) => a - b)) ===
+// 							JSON.stringify([nums[i], nums[j], nums[k]].sort((a, b) => a - b)),
+// 					);
+// 					if (!hasArray) {
+// 						result.push([nums[i], nums[j], nums[k]]);
+// 					}
+// 				}
+// 			}
+// 		}
+// 	}
+// 	return result;
+// }
+
+function threeSum(nums: number[]): number[][] {
+	const result: number[][] = [];
+	nums.sort((a, b) => a - b);
+
+	for (let i = 0; i < nums.length - 2; i++) {
+		if (i > 0 && nums[i] === nums[i - 1]) continue;
+
+		let left = i + 1;
+		let right = nums.length - 1;
+
+		while (left < right) {
+			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;
+}
+
+threeSum([-1, 0, 1, 2, -1, -4]); // [[-1,-1,2],[-1,0,1]]
+threeSum([0, 1, 1]); // []
+threeSum([0, 0, 0]); // [[0,0,0]]
+threeSum([
+	12, 5, -12, 4, -11, 11, 2, 7, 2, -5, -14, -3, -3, 3, 2, -10, 9, -15, 2, 14,
+	-3, -15, -3, -14, -1, -7, 11, -4, -11, 12, -15, -14, 2, 10, -2, -1, 6, 7, 13,
+	-15, -13, 6, -10, -9, -14, 7, -12, 3, -1, 5, 2, 11, 6, 14, 12, -10, 14, 0, -7,
+	11, -10, -7, 4, -1, -12, -13, 13, 1, 9, 3, 1, 3, -5, 6, 9, -4, -2, 5, 14, 12,
+	-5, -6, 1, 8, -15, -10, 5, -15, -2, 5, 3, 3, 13, -8, -13, 8, -5, 8, -6, 11,
+	-12, 3, 0, -2, -6, -14, 2, 0, 6, 1, -11, 9, 2, -3, -6, 3, 3, -15, -5, -14, 5,
+	13, -4, -4, -10, -10, 11,
+]); // [[-15,1,14],[-15,2,13],[-15,3,12],[-15,4,11],[-15,5,10],[-15,6,9],[-15,7,8],[-14,0,14],[-14,1,13],[-14,2,12],[-14,3,11],[-14,4,10],[-14,5,9],[-14,6,8],[-14,7,7],[-13,-1,14],[-13,0,13],[-13,1,12],[-13,2,11],[-13,3,10],[-13,4,9],[-13,5,8],[-13,6,7],[-12,-2,14],[-12,-1,13],[-12,0,12],[-12,1,11],[-12,2,10],[-12,3,9],[-12,4,8],[-12,5,7],[-12,6,6],[-11,-3,14],[-11,-2,13],[-11,-1,12],[-11,0,11],[-11,1,10],[-11,2,9],[-11,3,8],[-11,4,7],[-11,5,6],[-10,-4,14],[-10,-3,13],[-10,-2,12],[-10,-1,11],[-10,0,10],[-10,1,9],[-10,2,8],[-10,3,7],[-10,4,6],[-10,5,5],[-9,-5,14],[-9,-4,13],[-9,-3,12],[-9,-2,11],[-9,-1,10],[-9,0,9],[-9,1,8],[-9,2,7],[-9,3,6],[-9,4,5],[-8,-6,14],[-8,-5,13],[-8,-4,12],[-8,-3,11],[-8,-2,10],[-8,-1,9],[-8,0,8],[-8,1,7],[-8,2,6],[-8,3,5],[-8,4,4],[-7,-7,14],[-7,-6,13],[-7,-5,12],[-7,-4,11],[-7,-3,10],[-7,-2,9],[-7,-1,8],[-7,0,7],[-7,1,6],[-7,2,5],[-7,3,4],[-6,-6,12],[-6,-5,11],[-6,-4,10],[-6,-3,9],[-6,-2,8],[-6,-1,7],[-6,0,6],[-6,1,5],[-6,2,4],[-6,3,3],[-5,-5,10],[-5,-4,9],[-5,-3,8...

climbing-stairs/jiji-hoon96.ts

@@ -0,0 +1,19 @@
+function climbStairs(n: number): number {
+  if (n <= 2) return n;
+
+  let dp1 = 1;
+  let dp2 = 2;
+
+  for (let i = 3; i <= n; i++) {
+    let sum = dp1 + dp2;
+    dp1 = dp2;
+    dp2 = sum;
+  }
+
+  return dp2;
+}
+
+climbStairs(2); // 2
+climbStairs(3); // 3
+climbStairs(24); // 75025
+climbStairs(45); // 1836311903

product-of-array-except-self/jiji-hoon96.ts

@@ -0,0 +1,20 @@
+function productExceptSelf(nums: number[]): number[] {
+	const result = new Array(nums.length).fill(1);
+	let prefix = 1;
+	let suffix = 1;
+
+	for (let i = 0; i < nums.length; i++) {
+		result[i] = prefix;
+		prefix *= nums[i];
+	}
+
+	for (let j = nums.length - 1; j >= 0; j--) {
+		result[j] *= suffix;
+		suffix *= nums[j];
+	}
+
+	return result;
+}
+
+productExceptSelf([1, 2, 3, 4]); // [24,12,8,6]
+productExceptSelf([-1, 1, 0, -3, 3]); // [0,0,9,0,0]

valid-anagram/jiji-hoon96.ts

@@ -0,0 +1,26 @@
+function isAnagram(s: string, t: string): boolean {
+  if (s.length !== t.length) return false;
+
+  const list: Record<string, number> = {};
+  for (const key of s) {
+    list[key] = (list[key] ?? 0) + 1;
+  }
+
+  for (const key of t) {
+    if (key in list) {
+      list[key] -= 1;
+    }
+  }
+
+  for (const value in list) {
+    if (list[value] > 0) {
+      return false;
+    }
+  }
+
+  return true;
+}
+
+isAnagram("anagram", "nagaram"); // true
+isAnagram("rat", "car"); // false
+isAnagram("a", "ab"); // false

validate-binary-search-tree/jiji-hoon96.ts

@@ -0,0 +1,27 @@
+class TreeNode {
+	val: number;
+	left: TreeNode | null;
+	right: TreeNode | null;
+	constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+		this.val = val === undefined ? 0 : val;
+		this.left = left === undefined ? null : left;
+		this.right = right === undefined ? null : right;
+	}
+}
+
+function isValidBST(root: TreeNode | null): boolean {
+	function dfs(node: TreeNode | null, min: number, max: number) {
+		if (node === null) return true;
+
+		if (node.val <= min || node.val >= max) {
+			return false;
+		}
+
+		return dfs(node.left, min, node.val) && dfs(node.right, node.val, max);
+	}
+
+	return dfs(root, Number.NEGATIVE_INFINITY, Number.POSITIVE_INFINITY);
+}
+
+isValidBST([2, 1, 3]); // true
+isValidBST([5, 1, 4, null, null, 3, 6]); // false