Create 105-construct-binary-tree-from-preorder-and-inorder-traversal.js

Author: everthis

105-construct-binary-tree-from-preorder-and-inorder-traversal.js

@@ -0,0 +1,36 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {number[]} preorder
+ * @param {number[]} inorder
+ * @return {TreeNode}
+ */
+let pre
+let ins
+let inmap = {}
+const buildTree = function(preorder, inorder) {
+    pre = preorder
+    ins = inorder
+    for(let i = 0; i < inorder.length; i++) {
+      inmap[inorder[i]] = i
+    }
+    let root = helper(0,0,ins.length - 1)
+    return root
+};
+
+function helper(preStart, inStart, inEnd) {
+  if (preStart > pre.length -1 || inStart > inEnd) {
+    return null
+  }
+  let val = pre[preStart]
+  let root = new TreeNode(val)
+  let inIndex = inmap[val]
+  root.left = helper(preStart + 1, inStart, inIndex - 1)
+  root.right = helper(preStart+inIndex-inStart+1, inIndex+1, inEnd)
+  return root
+}