Problem:
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
Example 2:
Input: "()[]{}"
Output: true
Example 3:
Input: "(]"
Output: false
Example 4:
Input: "([)]"
Output: false
Example 5:
Input: "{[]}"
Output: true
思路：
Solution (C++):
bool isValid(string s) {
if (s.empty()) return true;
stack<char> stk{};
int len = s.length();
for (int i = 0; i < s.length(); ++i) {
if (s[i] == '(' || s[i] == '{' || s[i] == '[')
stk.push(s[i]);
else if (s[i] == ')') {
if (stk.empty() || stk.top() != '(') return false;
else stk.pop();
}
else if (s[i] == '}') {
if (stk.empty() || stk.top() != '{') return false;
else stk.pop();
}
else if (s[i] == ']') {
if (stk.empty() || stk.top() != '[') return false;
else stk.pop();
}
}
if (!stk.empty()) return false;
return true;
}
性能：
Runtime: 0 ms Memory Usage: 6.2 MB
思路：
Solution (C++):
性能：
Runtime: ms Memory Usage: MB
