lc-20

//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. 
// 
//
// 
// Example 1: 
//
// 
//Input: s = "()"
//Output: true
// 
//
// Example 2: 
//
// 
//Input: s = "()[]{}"
//Output: true
// 
//
// Example 3: 
//
// 
//Input: s = "(]"
//Output: false
// 
//
// 
// Constraints: 
//
// 
// 1 <= s.length <= 104 
// s consists of parentheses only '()[]{}'. 
// 
// Related Topics String Stack 
// 👍 13610 👎 616


//leetcode submit region begin(Prohibit modification and deletion)
class Solution {
    public boolean isValid(String s) {
        Stack<Character> myStack = new Stack<>();
        for (char ch : s.toCharArray()) {
            if (ch == '(' || ch == '[' || ch == '{') {
                myStack.push(ch);
            } else {
                if (myStack.isEmpty()) {
                    return false;
                }
                char top = myStack.peek();

                if ((top == '(' && ch == ')') ||
                        (top == '[' && ch == ']') ||
                        (top == '{' && ch == '}')) {
                    myStack.pop();
                } else {
                    return false;
                }
            }
        }

        return myStack.isEmpty();
    }
}
//leetcode submit region end(Prohibit modification and deletion)