Add some changes

Author: manojbaishya

.idea/misc.xml

@@ -2,6 +2,7 @@ Computer Science problems in Java.
 
 ### Migration status - dojo.net
 1. ArrayProblems.cs + ArrayProblemsTests.cs [WIP]
+2. Add Checker Framework - Clashes with Java Microbenchmark Harness annotation processor
 
 ## Backlog
 ### Problems

.idea/runConfigurations/Verify.xml

@@ -17,7 +17,7 @@ public int[] asteroidCollision(int[] asteroids) {
 
             if (Math.signum(stack.peek()) != sign) {
                 if (Math.signum(stack.peek()) > sign) {
-                    while (Math.signum(stack.peek()) > sign) {
+                    while (!stack.isEmpty() && Math.signum(stack.peek()) > sign) {
                         int top = stack.peek();
 
                         if (Math.abs(top) > Math.abs(num)) break;
@@ -42,4 +42,54 @@ public int[] asteroidCollision(int[] asteroids) {
 
         return stack.reversed().stream().mapToInt(i -> i).toArray();
     }
+
+    // public boolean isValid(String s) {
+    //     Deque<Bracket> stack = new ArrayDeque<>();
+    //     for (int i = 0; i < s.length(); i++) {
+    //         char c = s.charAt(i);
+    //         Bracket bracket = Bracket.fromSymbol(c);
+    //
+    //         if (stack.isEmpty()) {stack.push(bracket)}
+    //
+    //         ;
+    //     }
+    //
+    //     return false;
+    // }
+
+    enum Bracket {
+        PARENTHESES('(', ')'),
+        BRACES('{', '}'),
+        BRACKETS('[', ']');
+
+        Bracket(char openSymbol, char closeSymbol) {
+            this.openSymbol = openSymbol;
+            this.closeSymbol = closeSymbol;
+        }
+        private final char openSymbol;
+        public char getOpenSymbol() { return openSymbol; }
+
+        private final char closeSymbol;
+        public char getCloseSymbol() { return closeSymbol; }
+
+        enum State {
+            OPEN,
+            CLOSED
+        }
+
+        public char getSymbol(State state) { return state == State.OPEN ? openSymbol : closeSymbol; }
+
+        public static Bracket fromSymbol(char symbol) {
+            for (Bracket bracket : Bracket.values()) {
+                if (bracket.getOpenSymbol() == symbol || bracket.getCloseSymbol() == symbol) {
+                    return bracket;
+                }
+            }
+            throw new IllegalArgumentException("Unknown symbol: " + symbol);
+        }
+
+        public static boolean isMatching(char openSymbol, char closeSymbol) {
+            return fromSymbol(openSymbol).getCloseSymbol() == closeSymbol;
+        }
+    }
 }