How can a candidate have 10+ years or experience with C++ and let alone struggle with the most simple exercise!?

Thoughts from the inner me during an actual interview:

FOR FUCK SAKE, DUDE, PUT THAT "std::" IN FRONT OF YOUR "vector" AND IT WILL COMPILE!

USE ITERATORS GODDAMMIT INSTEAD OF THOSE FUCKING INDEXES. YOUR CODE IS FULL OF DAMN OVERFLOW ERRORS!

HAVE YOU EVER REALIZED THAT ARRAYS CAN BE EMPTY SOMETIMES?