20. Valid Parentheses (JAVA)
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:
Input: "()" Output: true
Example 2:
Input: "()[]{}" Output: true
Example 3:
Input: "(]" Output: false
Example 4:
Input: "([)]" Output: false
Example 5:
Input: "{[]}" Output: true
class Solution { public boolean isValid(String s) { Stack<Character> stack = new Stack<>(); //Primitive types such as char cannot be used as type parameters in Java. You need to use the wrapper type for(int i = 0; i < s.length(); i++){ if(s.charAt(i) == '(' || s.charAt(i) == '[' || s.charAt(i) == '{'){ stack.push(s.charAt(i)); } else if(s.charAt(i) == ')') { if(stack.empty() || stack.peek() != '(') return false; stack.pop(); } else if(s.charAt(i) == ']'){ if(stack.empty() || stack.peek() != '[') return false; stack.pop(); } else if(s.charAt(i) == '}'){ if(stack.empty() || stack.peek() != '{') return false; stack.pop(); } } if(!stack.empty()) return false; return true; } }