Determine whether a given string of parentheses is properly nested.

Brackets.java

package stacksandqueues;

import java.util.Stack;

public class Brackets {
	public int solution(String S) {
		if(!S.isEmpty() && S.length() % 2 != 0) {
			return 0;
		}
		
		Stack<Character> stack = new Stack<>();
		char[] toPush = new char[] {'{', '[', '('};
		
		for(char c : S.toCharArray()) {
			boolean isToPush = false;
			for(int i = 0; i < toPush.length; i++) {
				if(toPush[i] == c) {
					isToPush = true;
					break;
				}
			}
			
			if(isToPush) {
				stack.push(c);
			} else {
				if(stack.size() == 0) {
					return 0;
				} else if(!areOpositeChar(stack.pop(), c)) {
					return 0;
				}
			}
		}
		
		return stack.size() == 0 ? 1 : 0;
	}
	
	private boolean areOpositeChar(char a, char b) {
		if(a == '{' && b == '}') {
			return true;
		}
		else if(a == '[' && b == ']') {
			return true;
		} else if(a == '(' && b == ')') {
			return true;
		}
		
		return false;
	}
}