1249. 移除无效的括号

解法一

用栈来存储左括号，遇到左括号就入栈，遇到右括号就出栈。空栈直接遇到右括号说明不合法，删除。全部遍历完以后栈中剩余的左括号都是非法的，也要删除。

import java.util.Deque;
import java.util.LinkedList;
class Solution {
    public String minRemoveToMakeValid(String s) {
        StringBuilder stringBuilder = new StringBuilder(s);
        Deque<Integer> stack = new LinkedList<Integer>();
        int i = 0;
        while (i < stringBuilder.length()) {
            if ((stack.size() == 0) && (stringBuilder.charAt(i) == ')')) {
                stringBuilder.deleteCharAt(i);
            } else if (stringBuilder.charAt(i) == '(') {
                stack.push(i);
                ++i;
            } else if (stringBuilder.charAt(i) == ')') {
                stack.poll();
                ++i;
            } else {
                ++i;
            }
        }
        while (!stack.isEmpty()) {
            stringBuilder.deleteCharAt(stack.poll());
        }
        return stringBuilder.toString();
    }
}