Merge pull request DaleStudy#371 from highballplz/main

[highball] week2 solutions

Author: highballplz

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

@@ -0,0 +1,63 @@
+function TreeNode(val, left, right) {
+  this.val = val === undefined ? 0 : val;
+  this.left = left === undefined ? null : left;
+  this.right = right === undefined ? null : right;
+}
+
+const buildTree = function (preorder, inorder) {
+  if (preorder.length === 0) return null;
+
+  const rootNode = new TreeNode(preorder[0]);
+  const rootValueIndexAtInorder = inorder.indexOf(preorder[0]);
+
+  const leftLength = rootValueIndexAtInorder - 0;
+  const rightLength = inorder.length - 1 - rootValueIndexAtInorder;
+
+  const leftPreorder = preorder.slice(1, 1 + leftLength);
+  const leftInorder = inorder.slice(0, 0 + leftLength);
+  rootNode.left = buildTree(leftPreorder, leftInorder);
+
+  const rightPreorder = preorder.slice(
+    1 + leftLength,
+    1 + leftLength + rightLength
+  );
+  const rightInorder = inorder.slice(
+    rootValueIndexAtInorder + 1,
+    rootValueIndexAtInorder + 1 + rightLength
+  );
+  rootNode.right = buildTree(rightPreorder, rightInorder);
+
+  return rootNode;
+};
+
+function bfsTraversal(root) {
+  const treeValues = [];
+
+  const queue = [];
+  queue.push(root);
+
+  while (queue.length > 0) {
+    const n = queue.length;
+
+    for (let i = 0; i < n; i++) {
+      const currentNode = queue.shift();
+
+      if (currentNode) {
+        treeValues.push(currentNode.val);
+        queue.push(currentNode.left);
+        queue.push(currentNode.right);
+      } else {
+        treeValues.push(null);
+        queue.push(null);
+        queue.push(null);
+      }
+    }
+
+    if (queue.every((el) => el === null)) break;
+  }
+
+  return treeValues;
+}
+
+// console.log(bfsTraversal(buildTree([3, 9, 20, 15, 7], [9, 3, 15, 20, 7])));
+console.log(bfsTraversal(buildTree([1, 2], [2, 1])));

counting-bits/highball.js

@@ -0,0 +1,14 @@
+const countBits = function (n) {
+  const arr = new Array(n + 1);
+  arr[0] = 0;
+  if (n === 0) return arr;
+  arr[1] = 1;
+  if (n === 1) return arr;
+
+  for (i = 2; i <= n; i++) {
+    if (i % 2 === 0) arr[i] = arr[i / 2];
+    else arr[i] = arr[(i - 1) / 2] + 1;
+  }
+
+  return arr;
+};

encode-and-decode-strings/highball.js

@@ -0,0 +1,9 @@
+const encode = function (arr) {
+  const encodedStr = arr.reduce((acc, cur) => acc + "#" + cur);
+  return encodedStr;
+};
+
+const decode = function (str) {
+  const decodedArr = str.split("#");
+  return decodedArr;
+};

valid-anagram/highball.js

@@ -0,0 +1,16 @@
+const isAnagram = function (s, t) {
+  const sCharCount = new Array(26).fill(0);
+  const tCharCount = new Array(26).fill(0);
+
+  Array.from(s).forEach((char) => {
+    const charAsInt = char.charCodeAt(0) - 97;
+    sCharCount[charAsInt]++;
+  });
+
+  Array.from(t).forEach((char) => {
+    const charAsInt = char.charCodeAt(0) - 97;
+    tCharCount[charAsInt]++;
+  });
+
+  return sCharCount.reduce((acc, cur, i) => acc && cur === tCharCount[i], true);
+};