331. Verify Preorder Serialization Of A Binary Tree¶

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331. Verify Preorder Serialization of a Binary Tree

Medium

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 ','.

Solution¶

class Solution {
    public boolean isValidSerialization(String preorder) {
        int count = 1;
        String nodes[] = preorder.split(",");
        for (String temp : nodes) {
            if (count <= 0) return false;
            if (temp.equals("#")) count--;
            else count++;
        }
        return count == 0;
    }
}

Complexity Analysis¶

• Time Complexity: O(?)
• Space Complexity: O(?)

Approach¶

Detailed explanation of the approach will be added here