20. Valid Parentheses

Description

Given a string s containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

An input string is valid if:

1. Open brackets must be closed by the same type of brackets.
2. Open brackets must be closed in the correct order.
3. 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

Example 4:

Input: s = "([])"
Output: true

Constraints:

• 1 <= s.length <= \(10^{4}\)
• s consists of parentheses only '()[]{}'.

Solutions

I Stack

Complexity:

• Time complexity: \(O(n)\), where \(n\) is the length of the input string.
• Space complexity: \(O(n)\), where \(n\) is the length of the input string.

func isValid(s string) bool {
    stack := make([]rune, 0)
    m := map[rune]rune{
        ')': '(',
        ']': '[',
        '}': '{',
    }

    for _, c := range s {
        switch c {
        case '(', '[', '{':
            stack = append(stack, c)

        case ')', ']', '}':
            if len(stack) == 0 || stack[len(stack)-1] != m[c] {
                return false
            }
            stack = stack[:len(stack)-1]
        }
    }
    return len(stack) == 0
}