Create Verify_Preorder_Serialization_of_a_Binary_Tree.js

Author: ignacio-chiazzo

LeetcodeProblems/Verify_Preorder_Serialization_of_a_Binary_Tree.js

@@ -0,0 +1,71 @@
+/*
+Verify Preorder Serialization of a Binary Tree
+https://leetcode.com/problems/verify-preorder-serialization-of-a-binary-tree/
+
+One way to serialize a binary tree is to use pre-order traversal. When we encounter a non-null node, we record the node's value. If it is a null node, we record using a sentinel value such as #.
+
+     _9_
+    /   \
+   3     2
+  / \   / \
+ 4   1  #  6
+/ \ / \   / \
+# # # #   # #
+For example, the above binary tree can be serialized to the string "9,3,4,#,#,1,#,#,2,#,6,#,#", where # represents a null node.
+
+Given a string of comma separated values, verify whether it is a correct preorder traversal serialization of a binary tree. Find an algorithm without reconstructing the tree.
+
+Each comma separated value in the string must be either an integer or a character '#' representing null pointer.
+
+You may assume that the input format is always valid, for example it could never contain two consecutive commas such as "1,,3".
+
+Example 1:
+
+Input: "9,3,4,#,#,1,#,#,2,#,6,#,#"
+Output: true
+Example 2:
+
+Input: "1,#"
+Output: false
+Example 3:
+
+Input: "9,#,#,1"
+Output: false
+*/
+
+/**
+ * @param {string} preorder
+ * @return {boolean}
+ */
+var isValidSerialization = function(preorder) {
+  if(preorder.length === 1 && preorder.charAt(0) === "#")
+      return true;
+  
+  var depth = 0;
+  var iter = 0;
+  while(iter < preorder.length) {
+    if(preorder.charAt(iter) === "#") {
+      depth--;
+      iter += 2 
+    } else {
+      while(iter < preorder.length && preorder.charAt(iter) !== ",")
+        iter++
+      iter++;
+      depth = (depth === 0) ? depth + 2 : depth + 1;
+    }
+    if(iter < preorder.length && depth === 0)
+      return false;
+  }
+
+  return depth === 0;
+};
+
+var main = function() {
+  console.log(isValidSerialization(""));
+  console.log(isValidSerialization("#"));
+  console.log(isValidSerialization("9,3,4,#,#,1,#,#,2,#,6,#,#"));
+  console.log(isValidSerialization("9,#,92,#,#"));
+  console.log(isValidSerialization("9,3,4,#,#,1,#,#,#,2,#,6,#,#"));
+}
+
+module.exports.main = main;