一个输入字符串在以下情况下有效:
注意,空字符串也被认为是有效的。
下面是我的代码。
class Solution {
public boolean isValid(String s) {
Stack<Character> stack = new Stack<>();
int len = s.length();
for(int i=0;i<len;i++){
char cur = s.charAt(i);
if(cur=='{'){
stack.push('{');
}
else if(cur=='['){
stack.push('[');
}
else if(cur =='('){
stack.push('(');
}
else if(stack.peek()=='(' && cur==')'){
System.out.println(stack.peek());
stack.pop();
}
else if(stack.peek()=='[' && cur==']'){
stack.pop();
}
else if(stack.peek()=='{' && cur=='}'){
stack.pop();
}
}
if(stack.empty()) return true;
else return false;
}
}
当我把输入的内容写成:
")"
我得到一个错误:
java.util.EmptyStackException
在我检查条件的那行 ')'
. 请解释
我猜你是在解决 LeetCode 20,你可以简化一下你的代码。比如说,你可以用这个方法来简化你的代码。return stack.isEmpty();
够用 return
声明。
这里有更多可读的版本。
class Solution {
public boolean isValid(String baseString) {
Stack<Character> stack = new Stack<Character>();
for (char character : baseString.toCharArray()) {
if (character == '(')
stack.push(')');
else if (character == '{')
stack.push('}');
else if (character == '[')
stack.push(']');
else if (stack.isEmpty() || stack.pop() != character)
return false;
}
return stack.isEmpty();
}
}
class Solution {
public boolean isValid(String baseString) {
Stack<Character> stack = new Stack<Character>();
for (char character : baseString.toCharArray()) {
if (character == '(')
stack.push(')');
else if (character == '{')
stack.push('}');
else if (character == '[')
stack.push(']');
else if (stack.isEmpty() || stack.pop() != character)
return false;
}
return stack.isEmpty();
}
}
class Solution:
def isValid(self, base_string):
memo = {')': '(', '}': '{', ']': '['}
stack = [0]
for character in base_string:
if character in memo:
if stack.pop() != memo[character]:
return False
else:
stack.append(character)
return stack == [0]