How should I practice Valid Parentheses?

Start by reading the full statement, solve the visible examples, then compare the pattern against related EPAM onsite interview problems in FastPrep.

Is Valid Parentheses associated with EPAM?

FastPrep tags this as a EPAM onsite interview coding practice problem when the problem catalog has that company and stage context.

EPAM● EasyNEW GRADINTERNONSITE INTERVIEW

Given a string s that contains only the characters (, ), [, ], { and }, decide whether it is valid.

The string is valid when all of these rules hold:

Every opening bracket is closed by a closing bracket of the same type.
Brackets are closed in the right order: the bracket opened last is closed first.
Every closing bracket matches an opening bracket that comes before it.

Return true if s is valid, and false otherwise.

isValid(s: String) → boolean

s = "()[]{}"return = true

Each opening bracket is closed right away by a bracket of the same type.

s = "{[()]}"return = true

The brackets are nested. The last bracket opened, (, is closed first, then [, then {.

s = "([)]"return = false

The [ was opened after the (, so it must be closed first. The next closing bracket is ) while [ is still open, so the order is wrong.

s = "(("return = false

Two brackets are opened but neither is closed.