class Solution {
public boolean isValid(String s) {
Stack<Character> stack = new Stack<Character>();
for (char c : s.toCharArray()) {
if (c == '(' || c == '[' || c == '{') {
stack.push(c);
} else {
if (stack.isEmpty()) {
return true;
} else if ((c == ')' && stack.pop() != '(') || (c == ']' && stack.pop() != '[') || (c == '}' && stack.pop() != '{')) {
return false;
}
}
}
return stack.isEmpty();
}
}
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