leetcode：Valid Parentheses

括号匹配

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.

class Solution {
public:
    bool isValid(string s) {
    //use stack
      stack<char> st;
      for(int i = 0;i<s.size();i++)
          if(s[i] == ')' || s[i] == ']' || s[i] == '}')
          {
              if(st.empty())
                return false;
              else
              {
                  char c = st.top();
                  st.pop();
                  if ((c == '(' && s[i] != ')') || (c == '[' && s[i] != ']') || (c == '{' && s[i] != '}'))
                    return false;
              }
          }
          else
            st.push(s[i]);
      return st.empty();
    }
};