ValidParentheses.java

package stack;

import java.util.HashMap;
import java.util.Map;
import java.util.Stack;

/**
 * Created by gouthamvidyapradhan on 25/02/2017.
 * Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid.
 * <p>
 * The brackets must close in the correct order, "()" and "()[]{}" are all valid but "(]" and "([)]" are not.
 */
public class ValidParentheses {
    public static void main(String[] args) {
        System.out.println(hasBalancedBrackets("(h[e"));
    }

    private static Map<Character, Character> MAP = new HashMap<>();

    // METHOD SIGNATURE BEGINS, THIS METHOD IS REQUIRED
    public static int hasBalancedBrackets(String str) {
        if (str == null) return 1;

        MAP.put(')', '(');
        MAP.put('}', '{');
        MAP.put('>', '<');
        MAP.put(']', '[');

        Stack<Character> stack = new Stack<>();
        for (int i = 0, l = str.length(); i < l; i++) {
            switch (str.charAt(i)) {
                case '(':
                case '{':
                case '[':
                case '<':
                    stack.push(str.charAt(i));
                    break;

                case ')':
                case '}':
                case ']':
                case '>':
                    if (stack.isEmpty()) return 0;
                    char top = stack.pop();
                    if (top != MAP.get(str.charAt(i))) return 0;
                    break;

                default: //ignore
            }
        }
        return stack.isEmpty() ? 1 : 0;
    }
}