LeetCode : Valid Parentheses [java]

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：使用堆栈存储，遇到配对就弹出，为空则恰好全部配对成功。

import java.util.Stack;

public class Solution {
public boolean isValid(String s) {
Stack<Character> stack = new Stack<>();
for (int i = 0; i < s.length(); i++) {
char ch = s.charAt(i);
switch (ch) {
case ')':
if (!stack.isEmpty() && stack.peek() == '(') {
stack.pop();
} else {
stack.push(ch);
}
break;
case ']':
if (!stack.isEmpty() && stack.peek() == '[') {
stack.pop();
} else {
stack.push(ch);
}
break;
case '}':
if (!stack.isEmpty() && stack.peek() == '{') {
stack.pop();
} else {
stack.push(ch);
}
break;
default:
stack.push(ch);
}
}
return stack.isEmpty();
}
}