Construct Binary Tree from Preorder and Inorder Traversal / 중급

Author: oh-chaeyeon

oh-chaeyeon/5주차_트리/Construct_Binary_Tree_from_Preorder_and_Inorder_Traversal.js

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+/**
+ * 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) {
+  const inorderMap = new Map();
+  inorder.forEach((val, idx) => inorderMap.set(val, idx));
+
+  function build(preStart, preEnd, inStart, inEnd) {
+    if (preStart > preEnd || inStart > inEnd) return null;
+
+    const rootVal = preorder[preStart];
+    const root = new TreeNode(rootVal);
+    const inRootIndex = inorderMap.get(rootVal);
+    const leftSize = inRootIndex - inStart;
+
+    root.left = build(
+      preStart + 1,
+      preStart + leftSize,
+      inStart,
+      inRootIndex - 1
+    );
+    root.right = build(preStart + leftSize + 1, preEnd, inRootIndex + 1, inEnd);
+
+    return root;
+  }
+
+  return build(0, preorder.length - 1, 0, inorder.length - 1);
+};