ParenCheck.java

import java.util.LinkedList;

public class ParenCheck {
    static int OPENING = 1, CLOSING = -1;
    static int PAREN = 0, BRACKET = 1, BRACE = 2, PAIRING = 3;
    static String[] desc = { "()", "[]", "{}", "Pairing" }; 

    static int[] check(char[] s) {
        int[] stat = new int[4];
        int sym, type;
        LinkedList<Integer> stack = new LinkedList<Integer>();
        for(int i=0; i<s.length; i++) {
            switch(s[i]) {
            case '(': sym = PAREN; type = OPENING; break;
            case ')': sym = PAREN; type = CLOSING; break;
            case '[': sym = BRACKET; type = OPENING; break;
            case ']': sym = BRACKET; type = CLOSING; break;
            case '{': sym = BRACE; type = OPENING; break;
            case '}': sym = BRACE; type = CLOSING; break;
            default: continue;
            }
            stat[sym] += type;
            if(type == OPENING) {
                stack.push(sym);
            } else {
                if(!stack.isEmpty() && stack.peek() == sym)
                    stack.pop();
                else
                    stat[PAIRING]++;
            }
        }
        stat[PAIRING] += stack.size();
        return stat;
    }

    public static void main(String[] args) {
        if(args.length > 0) {
            int[] stat = check(args[0].toCharArray());
            for(int i=0; i<stat.length; i++)
                System.out.format("%s errors: %d\n", desc[i], Math.abs(stat[i]));
        }
    }

}