LeetCode-Easy020-Valid-Parentheses

Easy 020 Valid Parentheses

Description:

“()”“[]” “{}” 三种括号匹配问题，判断参数字符串是否满足匹配要求
如：“({[]})”true“[{})”false
Note: 空串为 true

My Solution:

1. • 括号匹配问题是栈的典型应用，遇到左括号，入栈，遇到右括号，看栈顶是否是相应的左括号，若不是，则 false
   • 时间复杂度 O(n)
   • 代码如下：

   •     public boolean isValid(String s) {if(s.length()==0){return true;}
          Stack<Character> stack = new Stack<>();
          for(char c:s.toCharArray()){if(c == '(' || c == '{' || c == '['){stack.push(c);
              }else if(stack.size()==0){return false;}
              else if(c == ')' && stack.peek() == '('){stack.pop();
              }else if(c == ']' && stack.peek() == '['){stack.pop();
              }else if(c == '}' && stack.peek() == '{'){stack.pop();
              }else
                  return false;
          }
          if(stack.size() == 0){return true;}
          return false;
      }

Fast Solution: