[재호] WEEK 02 Solutions

construct-binary-tree-from-preorder-and-inorder-traversal/wogha95.js

@@ -0,0 +1,33 @@
+// TC: O(N) - leetcode analyze 기준
+// SC: O(N)
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {number[]} preorder
+ * @param {number[]} inorder
+ * @return {TreeNode}
+ */
+var buildTree = function (preorder, inorder) {
+  if (inorder.length === 0) {
+    return null;
+  }
+
+  const rootValue = preorder[0];
+  const leftNodeLength = inorder.findIndex((value) => value === rootValue);
+  const leftNode = buildTree(
+    preorder.slice(1, 1 + leftNodeLength),
+    inorder.slice(0, leftNodeLength)
+  );
+  const rightNode = buildTree(
+    preorder.slice(1 + leftNodeLength),
+    inorder.slice(leftNodeLength + 1)
+  );
+  return new TreeNode(rootValue, leftNode, rightNode);
+};

counting-bits/wogha95.js

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+// TC: O(N)
+// SC: O(N)
+
+/**
+ * @param {number} n
+ * @return {number[]}
+ */
+var countBits = function (n) {
+  const result = [0];
+  let pointer = 0;
+  let lastPointer = 0;
+
+  for (let num = 1; num <= n; num++) {
+    result.push(result[pointer] + 1);
+
+    if (pointer === lastPointer) {
+      lastPointer = result.length - 1;
+      pointer = 0;
+    } else {
+      pointer += 1;
+    }
+  }
+
+  return result;
+};

decode-ways/wogha95.js

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+// TC: O(N)
+// SC: O(N)
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var numDecodings = function (s) {
+  if (s[0] === "0") {
+    return 0;
+  }
+  if (s.length === 1) {
+    return 1;
+  }
+
+  const dpTable = new Array(s.length).fill(0);
+  if (s[0] !== "0") {
+    dpTable[0] = 1;
+  }
+  if (s[1] !== "0") {
+    dpTable[1] += 1;
+  }
+  if (isValid(`${s[0]}${s[1]}`)) {
+    dpTable[1] += 1;
+  }
+
+  for (let index = 2; index < s.length; index++) {
+    if (s[index] !== "0") {
+      dpTable[index] += dpTable[index - 1];
+    }
+    if (s[index - 1] !== "0" && isValid(`${s[index - 1]}${s[index]}`)) {
+      dpTable[index] += dpTable[index - 2];
+    }
+  }
+
+  return dpTable[dpTable.length - 1];
+
+  function isValid(stringNumber) {
+    const number = Number(stringNumber);
+    if (number <= 0) {
+      return false;
+    }
+    if (27 <= number) {
+      return false;
+    }
+    return true;
+  }
+};

valid-anagram/wogha95.js

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+// TC: O(N * log N)
+// SC: O(N)
+
+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {boolean}
+ */
+var isAnagram = function(s, t) {
+  return s.split('').sort().join('') === t.split('').sort().join('');
+};