validParentheses.py

# Valid Parentheses

# 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 of the same type.
 

# Example 1:
# Input: s = "()"
# Output: true

# Example 2:
# Input: s = "()[]{}"
# Output: true

# Example 3:
# Input: s = "(]"
# Output: false

# Answers
def isValid(s):
    stack = [] 
    pairs = {
        '(': ')',
        '{': '}',
        '[': ']'
    }
    for i in s:
        if i in pairs:
            stack.append(i)
        elif len(stack) == 0 or i != pairs[stack.pop()]:
            return False

    return len(stack) == 0

s = "()[]{}"
print(isValid(s))