Given a string s containing just the characters (, ), {, }, [ and ], determine if the input string is valid. An input string is valid if: - Open brackets must be closed by the same type of brackets. - Open brackets must be closed in the correct order. - Every close bracket has a corresponding open bracket.

The step-through player is coming for this one. Two Sum has the full animation today; the rest are being authored in the admin.

Pythontime O(n) · space O(n)

def isValid(s: str) -> bool:
    stack = []
    pairs = {')': '(', '}': '{', ']': '['}
    for ch in s:
        if ch in '([{':
            stack.append(ch)
        elif not stack or stack[-1] != pairs[ch]:
            return False
        else:
            stack.pop()
    return len(stack) == 0

Next upBinary Search

Two Sum is free. Enroll to unlock every visualization and save where you stopped.Enroll free

Watch the video walkthrough