Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[‘ and ‘]’, determine if the input string is valid.

An input string is valid if:

Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.

• Example 1:

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Input: "()"
Output: true

• Example 2:

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Input: "()[]{}"
Output: true

• Example 3:

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Input: "(]"
Output: false

• Example 4:

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Input: "([)]"
Output: false

• Example 5:

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Input: "{[]}"
Output: true

判断是否串是否以给定的字符成对出现.

实现

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

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def (s: String): Boolean = {
    var res = s
    while (res.contains("()") || res.contains("{}") || res.contains("[]") ) {
      res = res.replaceAll("\(\)","")
      res = res.replaceAll("\{\}","")
      res = res.replaceAll("\[\]","")
    }
    res.equals("")
}

参考资料

• valid-parentheses