20 - Valid Parentheses

 JAVA

• class Solution {
      public boolean isValid(String s) {
          Deque<Character> stk = new ArrayDeque<>();
          for (char c : s.toCharArray()) {
              if (c == '(' || c == '{' || c == '[') {
                  stk.push(c);
              } else if (stk.isEmpty() || !match(stk.pop(), c)) {
                  return false;
              }
          }
          return stk.isEmpty();
      }
  
      private boolean match(char l, char r) {
          return (l == '(' && r == ')') || (l == '{' && r == '}') || (l == '[' && r == ']');
      }
  }

C++

• class Solution {
  public:
      bool isValid(string s) {
          string stk;
          for (char c : s) {
              if (c == '(' || c == '{' || c == '[')
                  stk.push_back(c);
              else if (stk.empty() || !match(stk.back(), c))
                  return false;
              else
                  stk.pop_back();
          }
          return stk.empty();
      }
  
      bool match(char l, char r) {
          return (l == '(' && r == ')') || (l == '[' && r == ']') || (l == '{' && r == '}');
      }
  };