day 26

Author: sachuverma

Leetcode Daily Challenge/August-2021/26. Verify Preorder Serialization of a Binary Tree.cpp

@@ -0,0 +1,67 @@
+/*
+Verify Preorder Serialization of a Binary Tree
+==============================================
+
+One way to serialize a binary tree is to use preorder 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 '#'.
+
+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 preorder, return true if it is a correct preorder traversal serialization of a binary tree.
+
+It is guaranteed that 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".
+Note: You are not allowed to reconstruct the tree.
+
+Example 1:
+Input: preorder = "9,3,4,#,#,1,#,#,2,#,6,#,#"
+Output: true
+
+Example 2:
+Input: preorder = "1,#"
+Output: false
+
+Example 3:
+Input: preorder = "9,#,#,1"
+Output: false
+
+Constraints:
+1 <= preorder.length <= 104
+preorder consist of integers in the range [0, 100] and '#' separated by commas ','.
+*/
+
+class Solution {
+public:
+    int j;
+    vector<string> arr;
+    
+    bool dfs() {
+        if(j >= arr.size()) return false;
+        
+        if(arr[j] == "#"){ 
+            j++;
+            return true;
+        }
+        
+        j++;
+        return dfs() && dfs();
+    }
+    
+    bool isValidSerialization(string s) {
+        string curr = "";
+        arr = vector<string> (0);
+        
+        for (int i = 0; i <= s.size(); ++i) {
+            if(i == s.size() || s[i] == ',') {
+                arr.push_back(curr);
+                curr = "";
+            }
+            else curr += s[i];
+        }
+        
+        j = 0;
+        return dfs() && j == arr.size();
+    }
+};

Leetcode Daily Challenge/August-2021/README.md

@@ -27,3 +27,6 @@
 | 23. | [Two Sum IV - Input is a BST](https://leetcode.com/explore/featured/card/august-leetcoding-challenge-2021/616/week-4-august-22nd-august-28th/3908/)                            |                  [cpp](./23.%20Two%20Sum%20IV%20-%20Input%20is%20a%20BST.cpp)                   |
 | 24. | [Complex Number Multiplication](https://leetcode.com/explore/featured/card/august-leetcoding-challenge-2021/616/week-4-august-22nd-august-28th/3917/)                            |                  [cpp](./24.%20Complex%20Number%20Multiplication.cpp)                   |
 | 25. | [Sum of Square Numbers](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/616/week-4-august-22nd-august-28th/3918/)                            |                  [cpp](./25.%20Sum%20of%20Square%20Numbers.cpp)                   |
+| 26. | [Verify Preorder Serialization of a Binary Tree](https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/616/week-4-august-22nd-august-28th/3920/) | [cpp](./26.%20Verify%20Preorder%20Serialization%20of%20a%20Binary%20Tree.cpp) |
+| 27. | []() | [cpp](./27.%20.cpp) |
+| 28. | []() | [cpp](./28.%20.cpp) |