20. 有效的括号

class Solution {
public:
bool isValid(string s) {
std::unordered_set leftBraces = {‘(’, ‘{’, ‘[’};
std::unordered_set rightBraces = {‘)’, ‘}’, ‘]’};
std::unordered_map<char, char> mp = {{‘)’, ‘(’}, {‘]’, ‘[’}, {‘}’, ‘{’}};
std::stack st;
for (const auto& ch: s) {
if (leftBraces.find(ch) != rightBraces.end()) {
st.push(ch);
continue;
}
if (rightBraces.find(ch) != rightBraces.end()) {
if(st.empty()) {
return false;
}
char top = st.top();
if (top == mp[ch]) {
st.pop();
} else {
return false;
}
}
}
return st.empty();
}
};