🚧 [105] a1

Author: enkr1

105/my_solution.js

@@ -0,0 +1,73 @@
+class TreeNode {
+  constructor(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) {
+  let tree = new TreeNode()
+
+  const buildNode = (node, order) => {
+    // if (null === node) return;
+    if (0 === order.length) return;
+    let curr = order[0],
+      tmpInorder = [...inorder],
+      inIdx = tmpInorder.indexOf(curr),
+      leftInorder = tmpInorder.splice(0, inIdx),
+      rightInorder = tmpInorder.splice(inIdx, tmpInorder.length - 1);
+
+    console.log(`-> inIdx:${inIdx}, curr:${curr}, order:${order}`);
+    console.log("from inorder:");
+    console.log(leftInorder, rightInorder);
+
+    // last idx from inorder of the left side is the end of the left leaves in pre
+    let tmpPreorder = [...order],
+      lastPreIdx = order.indexOf(leftInorder[leftInorder.length - 1]),
+      leftPreorder = tmpPreorder.splice(1, lastPreIdx),
+      rightPreorder = tmpPreorder.splice(lastPreIdx, tmpPreorder.length - 1);
+    console.log(">> PRE")
+    console.log(leftPreorder, rightPreorder)
+
+    node.val = curr;
+    console.log("node")
+    console.log(node)
+
+
+    console.log(order);
+    // if (inorder.indexOf(preorder[0]) < inIdx) {
+    //   console.log(`-> l ${inorder.indexOf(preorder[0])} < ${inIdx}`);
+    if (leftPreorder.length > 0) {
+      //   // yes it is left leave
+      node.left = new TreeNode(order[1]);
+      console.log(`Adding ${order[1]} to left`)
+      buildNode(node.left, leftPreorder);
+    }
+
+    if (rightPreorder.length > 0) {
+      //   console.log(`-> r ${inorder.indexOf(preorder[0])} > ${inIdx}`);
+      console.log(`Adding ${order[lastPreIdx + 1]} to right`)
+      node.right = new TreeNode(order[lastPreIdx + 1]);
+      buildNode(node.right, rightPreorder);
+    }
+  }
+
+  buildNode(tree, [...preorder]);
+
+  return tree;
+};
+
+let x =
+  // buildTree([3, 9, 20, 15, 7], [9, 3, 15, 20, 7])
+  // buildTree([-1], [-1])
+  buildTree([1, 2, 3], [3, 2, 1])
+// buildTree([3, 9, 8, 6, 7, 20], [6, 8, 9, 7, 3, 20])
+
+console.log("Result")
+console.log(x);

105/solution.js

@@ -39,6 +39,7 @@
 - [100. Same Tree](./100/)
 - [102. Binary Tree Level Order Traversal](./102/)
 - [104. Maximum Depth of Binary Tree](./104/)
+- [105. Construct Binary Tree from Preorder and Inorder Traversal](./105/)
 - [121. Best Time to Buy and Sell Stock](./121/)
 - [128. Longest Consecutive Sequence](./128/)
 - [133. Clone Graph](./133/)
@@ -142,7 +143,7 @@ Batch create:
 NOTE: JS IS HERE
 -->
 ```ssh
-chapter=102 && mkdir ./$chapter && touch ./$chapter/my_solution.js && touch ./$chapter/solution.js && alias x="node ./$chapter/my_solution.js"
+chapter=105 && mkdir ./$chapter && touch ./$chapter/my_solution.js && touch ./$chapter/solution.js && alias x="node ./$chapter/my_solution.js"
 ```
 > then you can use `x` for quick debug.