[hyer0705] WEEK 15 solutions

alien-dictionary/hyer0705.ts

@@ -0,0 +1,63 @@
+export class Solution {
+  alienOrder(words: string[]): string {
+    const indegree = new Map<string, number>();
+    const graph = new Map<string, Set<string>>();
+
+    for (const word of words) {
+      for (const ch of word) {
+        if (graph.has(ch)) continue;
+        graph.set(ch, new Set<string>());
+        indegree.set(ch, 0);
+      }
+    }
+
+    for (let i = 0; i < words.length - 1; i++) {
+      const word1 = words[i];
+      const word2 = words[i + 1];
+
+      let pointer = 0;
+      while (pointer < word1.length && pointer < word2.length && word1[pointer] === word2[pointer]) {
+        pointer++;
+      }
+
+      if (pointer < word1.length && pointer === word2.length) {
+        return "";
+      }
+
+      if (pointer < word1.length && pointer < word2.length) {
+        const neighbors = graph.get(word1[pointer])!;
+        if (!neighbors.has(word2[pointer])) {
+          neighbors.add(word2[pointer]);
+          indegree.set(word2[pointer], (indegree.get(word2[pointer]) || 0) + 1);
+        }
+      }
+    }
+
+    const queue: string[] = [];
+    const result: string[] = [];
+
+    for (const [ch, degree] of indegree) {
+      if (degree === 0) {
+        queue.push(ch);
+      }
+    }
+
+    while (queue.length > 0) {
+      const current = queue.shift()!;
+      result.push(current);
+
+      for (const neighbor of graph.get(current) || []) {
+        indegree.set(neighbor, (indegree.get(neighbor) || 0) - 1);
+        if (indegree.get(neighbor) === 0) {
+          queue.push(neighbor);
+        }
+      }
+    }
+
+    if (indegree.size === result.length) {
+      return result.join("");
+    }
+
+    return "";
+  }
+}

construct-binary-tree-from-preorder-and-inorder-traversal/hyer0705.ts

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+/**
+ * Definition for a binary tree node.
+ * 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)
+ *     }
+ * }
+ */
+
+// 37ms
+// Time Complexity: O(n^2), n: 노드의 수
+// Space Complexity: O(h), h: 트리의 높이
+function buildTree(preorder: number[], inorder: number[]): TreeNode | null {
+  if (preorder.length === 0 || inorder.length === 0) return null;
+
+  const root = preorder[0];
+
+  const rootIdx = inorder.findIndex((el) => el === root);
+
+  const leftInorder = inorder.slice(0, rootIdx);
+  const leftPreorder = preorder.slice(1, leftInorder.length + 1);
+
+  const rightInorder = inorder.slice(rootIdx + 1);
+  const rightPreorder = preorder.slice(leftInorder.length + 1);
+
+  const rootNode = new TreeNode(root);
+
+  rootNode.left = buildTree(leftPreorder, leftInorder);
+  rootNode.right = buildTree(rightPreorder, rightInorder);
+
+  return rootNode;
+}
+
+// 3ms
+// Time Complexity: O(n), n: 노드의 수
+// Space Complexity: O(n), n: 노드의 수
+function buildTree(preorder: number[], inorder: number[]): TreeNode | null {
+  if (preorder.length === 0 || inorder.length === 0) return null;
+
+  const indexMap = new Map<number, number>();
+  inorder.forEach((node, idx) => indexMap.set(node, idx));
+
+  const build = (preStart: number, preEnd: number, inStart: number, inEnd: number): TreeNode | null => {
+    if (preStart > preEnd || inStart > inEnd) return null;
+
+    const rootVal = preorder[preStart];
+    const rootIdx = indexMap.get(rootVal);
+
+    const leftSize = rootIdx - inStart;
+
+    const root = new TreeNode(rootVal);
+    root.left = build(preStart + 1, preStart + leftSize, inStart, rootIdx - 1);
+    root.right = build(preStart + leftSize + 1, preEnd, rootIdx + 1, inEnd);
+
+    return root;
+  };
+
+  return build(0, preorder.length - 1, 0, inorder.length - 1);
+}

longest-palindromic-substring/hyer0705.ts

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+// Time Complexity: O(n^2), n: s의 길이
+// Space Complexity: O(1)
+function longestPalindrome(s: string): string {
+  const expandAroundCenter = (s: string, left: number, right: number): [number, number] => {
+    while (left >= 0 && right < s.length && s[left] === s[right]) {
+      left--;
+      right++;
+    }
+
+    return [left + 1, right - 1];
+  };
+
+  let longest = "";
+  for (let i = 0; i < s.length; i++) {
+    const [s1, e1] = expandAroundCenter(s, i, i);
+    const [s2, e2] = expandAroundCenter(s, i, i + 1);
+
+    const odd = e1 - s1 + 1;
+    const even = e2 - s2 + 1;
+
+    if (longest.length < odd) {
+      longest = s.slice(s1, e1 + 1);
+    }
+
+    if (longest.length < even) {
+      longest = s.slice(s2, e2 + 1);
+    }
+  }
+
+  return longest;
+}

rotate-image/hyer0705.ts

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+/**
+ Do not return anything, modify matrix in-place instead.
+ */
+// Time Complexity: O(n^2), n: matrix의 한 변의 길이
+// Space Complexity: O(1)
+function rotate(matrix: number[][]): void {
+  const n = matrix.length;
+
+  for (let i = 0; i < n; i++) {
+    for (let j = i + 1; j < n; j++) {
+      [matrix[i][j], matrix[j][i]] = [matrix[j][i], matrix[i][j]];
+    }
+  }
+
+  for (let i = 0; i < n; i++) {
+    for (let j = 0; j < Math.floor(n / 2); j++) {
+      [matrix[i][j], matrix[i][n - j - 1]] = [matrix[i][n - j - 1], matrix[i][j]];
+    }
+  }
+}

subtree-of-another-tree/hyer0705.ts

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+/**
+ * Definition for a binary tree node.
+ * 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)
+ *     }
+ * }
+ */
+
+// Time Complexity: O(m * n), m: root의 노드 수, n: subRoot의 노드 수
+// Space Complexity: O(h), h: root의 높이
+function isSubtree(root: TreeNode | null, subRoot: TreeNode | null): boolean {
+  if (!root) return false;
+
+  const isSameTree = (root: TreeNode | null, subRoot: TreeNode | null): boolean => {
+    if (!root && !subRoot) return true;
+    if (!root || !subRoot) return false;
+    if (root.val !== subRoot.val) return false;
+
+    return isSameTree(root.left, subRoot.left) && isSameTree(root.right, subRoot.right);
+  };
+
+  const current = isSameTree(root, subRoot);
+  const left = isSubtree(root.left, subRoot);
+  const right = isSubtree(root.right, subRoot);
+
+  return current || left || right;
+}