20. Valid Parentheses
20. Valid Parentheses
难度: Easy
刷题内容
原题连接 * https://leetcode-cn.com/problems/valid-parentheses/
内容描述
Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
An input string is valid if:
Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.
### Example
1. Input: "()" -> Output: true
2. Input: "()[]{}" -> Output: true
3. Input: "(]" -> Output: false
4. Input: "([)]" -> Output: false
5. Input: "{[]}" -> Output: true
解题方案
思路：
利用栈先进后出的先天优势，解决匹配问题。
bool isValid(string s) {
stack<char> stacks;
for(int i=0;i<s.length();i++){
if(s[i]=='('||s[i]=='{'||s[i]=='[')
stacks.push(s[i]);
else if(stacks.empty()){
return false;
}else{
char ch = stacks.top();
stacks.pop();
if(s[i]==')'&&ch=='('||s[i]==']'&&ch=='['||s[i]=='}'&&ch=='{')
continue;
else
return false;
}
}
if(stacks.empty())
return true;
else
return false;
}
