leetcode 栈和队列类型题

1，Valid Parentheses

 1 bool isVaild1(string& s) {  // 直接列举，不易扩展
 2     stack<char> stk;
 3     for (int i = 0; i < s.length(); ++i) {
 4         if (stk.empty())
 5             stk.push(s[i]);
 6         else {
 7             char top = stk.top();
 8             if (top == '(' && s[i] == ')' || top == '{' && s[i] == '}' || top == '[' && s[i] == ']')
 9                 stk.pop();
10         }
11     }
12     if (stk.empty())
13         return true;
14     else
15         return false;
16 }
17 
18 bool isValid2(string& s) {
19     string left = "([{";
20     string right = ")]}";
21     stack<char> stk;
22 
23     for (auto c = s.begin(); c != s.end(); ++c) {
24         if (left.find(*c) != string::npos)
25             stk.push(*c);
26         else {
27             if (stk.empty() || stk.top() != left[right.find(*c)])
28                 return false;
29             else
30                 stk.pop();
31         }
32     }
33     return stk.empty();
34 }

isVaild