LeetCode20 Valid Parentheses

题目要求:

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.

这道题目开始走了一些弯路,后来看到参考网友的答案才做出来

使用的是Stack这种数据结构

public class new_solution {

public boolean isValid(String s) {

if(s.length() == 0 || s.length() % 2 != 0) return false;

Stack<Character> stack = new Stack<Character>();
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) == ')' && !stack.empty() && stack.peek() == '(') stack.pop();
else if(s.charAt(i) == ']' && !stack.empty() && stack.peek() == '[') stack.pop();
else if(s.charAt(i) == '}' && !stack.empty() && stack.peek() == '{') stack.pop();
else return false;
}
return stack.isEmpty();
}

}