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package stack; import java.util.HashMap; import java.util.Stack; class Solution1 { HashMap hmLambda = new HashMap() { { put('(',')'); put('[', ']'); put('{', '}'); }}; public boolean isValid(String s) { if(s.length() % 2 != 0){ return false; } Stack stack = new Stack(); char[] charArray = s.toCharArray(); for(Character k : charArray){ if(hmLambda.containsKey(k)){ stack.push(k); }else{ if(stack.isEmpty() || k != hmLambda.get(stack.pop())){ return false; } } } return true; } public static void main(String[] args) { boolean valid = new Solution1().isValid("()"); System.out.println(valid); } }