Write a Java program to validate parentheses.

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.

Java program to Validate Parentheses

public static boolean isValid(String s) {
HashMap<Character, Character> map = new HashMap<Character, Character>();
map.put(’(’, ’)’);
map.put(’[’, ’]’);
map.put(’{’, ’}’);
Stack<Character> stack = new Stack<Character>();
for (int i = 0; i < s.length(); i++) {
char curr = s.charAt(i);
if (map.keySet().contains(curr)) {
stack.push(curr);
} else if (map.values().contains(curr)) {
if (!stack.empty() && map.get(stack.peek()) == curr) {
stack.pop();
} else {
return false;
}
}
}
return stack.empty();
}

Solution 2

public static boolean isValid(String s) {
char[] charArray = s.toCharArray();
HashMap<Character, Character> map = new HashMap<Character, Character>();
map.put(’(’, ’)’);
map.put(’[’, ’]’);
map.put(’{’, ’}’);
Stack<Character> stack = new Stack<Character>();
for (Character c : charArray) {
if (map.keySet().contains(c)) {
stack.push(c);
} else if (map.values().contains(c)) {
if (!stack.isEmpty() && map.get(stack.peek()) == c) {
stack.pop();
} else {
return false;
}
}
}
return stack.isEmpty();
}