【LeetCode】020. Valid Parentheses

Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.

The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.

题解：

　　括号匹配问题，与出现顺序有关，联想到栈和队列。

Solution 1

 class Solution {
 public:
     bool isValid(string s) {
         if (s.empty())
             return true;
         stack<char> st;

         for (int i = ; i < s.size(); ++i) {
             char cur = s[i];
             if (cur == '[' || cur == '(' || cur == '{') {
                 st.push(cur);
                 continue;
             }
             if (st.empty())
                 return false;
             if (cur == ']' && st.top() != '['
                 || cur == '}' && st.top() != '{'
                 || cur == ')' && st.top() != '(')
                 return false;
             st.pop();
         }

         return st.empty();
     }
 };