Valid Parentheses

Description:

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.

 

Code:

    bool isValid(string str) {

        size_t n = str.length();

        stack<char>s;

        for (int i = 0; i < n; ++i)

        {

            //要注意及时检查栈是否为空，因为不能对空栈调用top函数

            if (s.empty() || str[i] == '(' || str[i] == '{' || str[i] == '[')

                s.push(str[i]);

            else

            {

                char c = s.top();

                if ( (c== '(' && str[i] == ')')

                    || (c== '[' && str[i] == ']')

                    || (c== '{' && str[i] == '}') )

                    s.pop();

                else

                    return false;

            }

        }

        return (s.empty()==true)?true:false;

    }