算法Sedgewick第四版-第1章基础-010一检查括号是否成对出现

/******************************************************************************
 *  Compilation:  javac Parentheses.java
 *  Execution:    java Parentheses
 *  Dependencies: In.java Stack.java
 *
 *  Reads in a text file and checks to see if the parentheses are balanced.
 *
 *  %  java Parentheses
 *  [()]{}{[()()]()}
 *  true
 *
 *  % java Parentheses
 *  [(]) 
 *  false
 *
 ******************************************************************************/

public class Parentheses {
    private static final char LEFT_PAREN     = '(';
    private static final char RIGHT_PAREN    = ')';
    private static final char LEFT_BRACE     = '{';
    private static final char RIGHT_BRACE    = '}';
    private static final char LEFT_BRACKET   = '[';
    private static final char RIGHT_BRACKET  = ']';

    public static boolean isBalanced(String s) {
        Stack<Character> stack = new Stack<Character>();
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == LEFT_PAREN)   stack.push(LEFT_PAREN);
            if (s.charAt(i) == LEFT_BRACE)   stack.push(LEFT_BRACE);
            if (s.charAt(i) == LEFT_BRACKET) stack.push(LEFT_BRACKET);

            if (s.charAt(i) == RIGHT_PAREN) {
                if (stack.isEmpty())           return false;
                if (stack.pop() != LEFT_PAREN) return false;
            }

            else if (s.charAt(i) == RIGHT_BRACE) {
                if (stack.isEmpty())           return false;
                if (stack.pop() != LEFT_BRACE) return false;
            }

            else if (s.charAt(i) == RIGHT_BRACKET) {
                if (stack.isEmpty())             return false;
                if (stack.pop() != LEFT_BRACKET) return false;
            }
        }
        return stack.isEmpty();
    }


    public static void main(String[] args) {
        In in = new In();
        String s = in.readAll().trim();
        StdOut.println(isBalanced(s));
    }
}

/*************************************************************************
 * 
 * % java Ex_1_3_04
 * [()]{}{[()()]()}
 * true
 * 
 * % java Ex_1_3_04
 * [(])
 * false
 * 
 *************************************************************************/

public class Ex_1_3_04
{
    public static boolean isBalanced(String s)
    {
        Stack<Character> open = new Stack<Character>();
        int n = s.length();
        
        for (int i = 0; i < n; i++)
        {
            char c = s.charAt(i);
            
            if (c == '(' || c == '[' || c == '{')
                open.push(c);
            else if ((c == ')' && (open.isEmpty() || open.pop() != '(')) ||
                     (c == ']' && (open.isEmpty() || open.pop() != '[')) ||
                     (c == '}' && (open.isEmpty() || open.pop() != '{')))
                return false;
        }
        
        return open.isEmpty();
    }
    
    public static void main(String[] args)
    {
        String s = StdIn.readAll().trim();
        
        StdOut.println(isBalanced(s));
    }
}