Adding the 5th assignment problem statement and a first crack at the 5th...

Adding the 5th assignment problem statement and a first crack at the 5th assignment method they want us to implement.

fifthassignment/src/main/java/com/ds/fifthassignment/App.java

-package com.ds.fifthassignment;
-
-/**
- * Hello world!
- *
- */
-public class App 
-{
-    public static void main( String[] args )
-    {
-        System.out.println( "Hello World!" );
-    }
-}

fifthassignment/src/main/java/com/ds/fifthassignment/Application.java

+package com.ds.fifthassignment;
+
+import java.util.Stack;
+
+public class Application {
+	public class Bracket {
+		public static final char LEFT_P = '('; 
+		public static final char RIGHT_P = ')'; 
+		public static final char LEFT_B = '['; 
+		public static final char RIGHT_B = ']';
+		public static final char LEFT_CURL_B = '{';
+        public static final char RIGHT_CURL_B = '}'; 
+        
+        public static final String LEFT = String(
+            [LEFT_P, LEFT_B, LEFT_CURL_B]);
+        
+        public static final String RIGHT = String(
+            [RIGHT_P, RIGHT_B, RIGHT_CURL_B]);
+		
+	}
+
+	
+	public static void main(String[] args) {
+		char[] input1 = 	input1 = "[(4+5+1) x (4 / 2)]".toCharArray(); 
+		char[] input2 = "[(4+5+1) x (4 / 2]".toCharArray(); 
+		System.out.println(isValid(input1));
+		System.out.println(isValid(input2));
+	}
+    
+    /**
+     * validates the brackets of a char[]
+     * 
+     * @param input a char[] to validate
+     */
+	public static boolean isValid(char[] input) {
+        Stack s = new Stack();
+
+        for (char c: input){
+            if( Bracket.RIGHT.indexOf(c) != -1 ){
+                //right (closing) bracket
+                if(s.isEmpty() || !s.pop().equals(getPair(c))){
+                    return false;
+                }
+            }else if(Bracket.LEFT.indexOf(c) != -1){
+                //left (opening) bracket
+                s.push(c);
+            }
+        }
+        if(!s.isEmpty()){
+            return false;
+        }
+		return true;
+	}
+	
+	public static char getPair(char symbol) {
+		if(symbol == Bracket.LEFT_B) return Bracket.RIGHT_B; 
+		if(symbol == Bracket.RIGHT_B) return Bracket.LEFT_B;
+		
+		if(symbol == Bracket.RIGHT_P) return Bracket.LEFT_P; 
+		if(symbol == Bracket.LEFT_P) return Bracket.RIGHT_P;
+		
+		if(symbol == Bracket.LEFT_CURL_B) return Bracket.RIGHT_CURL_B; 
+		if(symbol == Bracket.RIGHT_CURL_B) return Bracket.LEFT_CURL_B;
+		
+		else return '0'; 
+	}
+}
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