[LeetCode]20. Valid Parentheses

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.

解：栈的基本使用。

public class Solution {
public boolean isValid(String s) {
Stack<String> stack = new Stack<>();

char cur,top;

for (int i = 0;i < s.length();i++){

cur = s.charAt(i);

if (cur == '(' || cur == '[' || cur == '{'){
stack.push(String.valueOf(cur));
}else {
if (stack.empty()) return false;

top = stack.pop().charAt(0);

if (cur == ')' && top != '(')  return false;
if (cur == ']' && top != '[')  return false;
if (cur == '}' && top != '{')  return false;
}
}

if (!stack.empty()) return false;

return true;

}
}