1、week3
1.1、有效的括号
public boolean isValid(String s) {
Deque<Character> stack = new Deque<>();
char[] chars = s.toCharArray();
for (char c : chars) {
if (c == '(' || c == '[' || c == '{') stack.addLast(c);
else {
if (stack.isEmpty()) return false;
char top = stack.removeLast();
if (c == ')' && top != '(') return false;
if (c == ']' && top != '[') return false;
if (c == '}' && top != '{') return false;
}
}
return stack.isEmpty();
}