# Posts tagged as “iterative”

The Tribonacci sequence Tn is defined as follows:

T0 = 0, T1 = 1, T2 = 1, and Tn+3 = Tn + Tn+1 + Tn+2 for n >= 0.

Given n, return the value of Tn.

Example 1:

Input: n = 4
Output: 4
Explanation:
T_3 = 0 + 1 + 1 = 2
T_4 = 1 + 1 + 2 = 4


Example 2:

Input: n = 25
Output: 1389537


Constraints:

• 0 <= n <= 37
• The answer is guaranteed to fit within a 32-bit integer, ie. answer <= 2^31 - 1.

## Solution: DP

Time complexity: O(n)
Space complexity: O(n) -> O(1)

# Problem

Given a binary tree, return the inorder traversal of its nodes’ values.

For example:
Given binary tree [1,null,2,3],

   1
\
2
/
3


return [1,3,2].

Note: Recursive solution is trivial, could you do it iteratively?

# Solution: Recursion

Time complexity: O(n)

Space complexity: O(h)

C++

# Problem:

Given a binary tree, return the postorder traversal of its nodes’ values.

For example:
Given binary tree {1,#,2,3},

return [3,2,1].

Note: Recursive solution is trivial, could you do it iteratively?  