題目:

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

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

 

思路:

檢查輸入的字串的括號是否有成對出現.

此種類型透過堆疊能夠快速且有效地進行比較.

 

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public static boolean isValid(String s) {
	Stack<Character> stack = new Stack<>();
	if(s.length()%2!=0)
		return false;
	
	for(int i=0;i<s.length();i++){
		char c = s.charAt(i);
		
		if(c == '(')
			stack.push(')');
		else if(c == '[')
			stack.push(']');
		else if(c == '{')
			stack.push('}');
		else{
			if(stack.isEmpty())
				return false;
			
			char t = stack.pop();
			if(t != c)
				return false;
		}
		
	}
	if(stack.empty())
		return true;
	else
		return false;
}

 

 

 

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