LeetCode 20. Valid Parentheses

Stack

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.

Example 1:

Input: s = "()"
Output: true

Example 2:

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

Example 3:

Input: s = "(]"
Output: false

Example 4:

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

Example 5:

Input: s = "{[]}"
Output: true

Constraints:

• 1 <= s.length <= 104

• s consists of parentheses only '()[]{}'.

Solution:

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class Solution {
public:
    bool isValid(string s) {
        stack<char> container;
        for (char c : s) {
            if (container.empty()) {
                container.push(c);
            } else {
                if (c == '(' || c == '{' || c == '[') {
                    container.push(c);
                } else {
                    char v = container.top();
                    if ( (c == ')' && v == '(') || (c == '}' && v == '{') || (c == ']' && v == '[')) {
                        container.pop();
                    } else {
                        return false;
                    }
                }
            }
        }
        return container.empty();
    }
    
};