Create 889-construct-binary-tree-from-preorder-and-postorder-traversal.js

Author: everthis

889-construct-binary-tree-from-preorder-and-postorder-traversal.js

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+/**
+
+Return any binary tree that matches the given preorder and postorder traversals.
+Values in the traversals pre and post are distinct positive integers.
+
+Example 1:
+
+Input: pre = [1,2,4,5,3,6,7], post = [4,5,2,6,7,3,1]
+Output: [1,2,3,4,5,6,7]
+ 
+Note:
+
+1 <= pre.length == post.length <= 30
+pre[] and post[] are both permutations of 1, 2, ..., pre.length.
+It is guaranteed an answer exists.
+If there exists multiple answers, you can return any of them.
+
+*/
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {number[]} pre
+ * @param {number[]} post
+ * @return {TreeNode}
+ */
+const constructFromPrePost = function(pre, post) {
+  let i = 0,
+    j = 0
+  return (function dfs() {
+    let val = pre[i++]
+    let node = new TreeNode(val)
+    if (val !== post[j]) node.left = dfs()
+    if (val !== post[j]) node.right = dfs()
+    j++
+    return node
+  })()
+}