I applied online for the position and received an email the next day allowing me to schedule an on-campus interview. Although I graduated last year, I believe they saw my university's name on my resume.

At the school, there were three teams of interviewers, with two interviewers per team. The interview lasted about an hour. Initially, they asked about some recent projects. Afterward, they asked me to code solutions to the two problems below on paper.

I arrived at correct solutions for both problems, but I think I made a mistake by stating an incorrect runtime estimate for one of the solutions. However, I did correct myself soon after realizing my error.

Provided a binary tree, write a function to return the sum of all nodes at or below a certain specified level in the tree.

Provided a string with any of the following characters: ( , ) , { , } , [ , ] , write a function to figure out if it's 'balanced'. For example, "( { } )" is balanced, "( { ) }" is not.