Merge pull request TheAlgorithms#1029 from shellhub/dev

yanglbme · web-flow · commit eec7f3e507ed · 2019-10-13T09:41:43.000+08:00
update BalancedBrackets
diff --git a/DataStructures/Stacks/BalancedBrackets.java b/DataStructures/Stacks/BalancedBrackets.java
@@ -1,10 +1,8 @@
-package data_structures.Stacks;
+package DataStructures.Stacks;
 
-import java.util.Scanner;
 import java.util.Stack;
 
 /**
- *
  * The nested brackets problem is a problem that determines if a sequence of
  * brackets are properly nested. A sequence of brackets s is considered properly
  * nested if any of the following conditions are true: - s is empty - s has the
@@ -15,71 +13,69 @@
  * returns true if S is nested and false otherwise.
  *
  * @author akshay sharma
- * @date: 2017-10-17
  * @author <a href="https://github.com/khalil2535">khalil2535<a>
- *
+ * @author shellhub
  */
 class BalancedBrackets {
 
     /**
+     * Check if {@code leftBracket} and {@code rightBracket} is paired or not
+     *
+     * @param leftBracket   left bracket
+     * @param rightBracket right bracket
+     * @return {@code true} if {@code leftBracket} and {@code rightBracket} is paired,
+     * otherwise {@code false}
+     */
+    public static boolean isPaired(char leftBracket, char rightBracket) {
+        char[][] pairedBrackets = {
+                {'(', ')'},
+                {'[', ']'},
+                {'{', '}'},
+                {'<', '>'}
+        };
+        for (char[] pairedBracket : pairedBrackets) {
+            if (pairedBracket[0] == leftBracket && pairedBracket[1] == rightBracket) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    /**
+     * Check if {@code brackets} is balanced
      *
-     * @param s
-     * @return
+     * @param brackets the brackets
+     * @return {@code true} if {@code brackets} is balanced, otherwise {@code false}
      */
-    static boolean is_balanced(String s) {
+    public static boolean isBalanced(String brackets) {
+        if (brackets == null) {
+            throw new IllegalArgumentException("brackets is null");
+        }
         Stack<Character> bracketsStack = new Stack<>();
-        char[] text = s.toCharArray();
-        for (char x : text) {
-            switch (x) {
-                case '{':
-                case '<':
+        for (char bracket : brackets.toCharArray()) {
+            switch (bracket) {
                 case '(':
                 case '[':
-                    bracketsStack.push(x);
+                case '{':
+                    bracketsStack.push(bracket);
                     break;
-                case '}':
-                    if (!bracketsStack.empty() && bracketsStack.pop() == '{') {
-                        break;
-                    } else {
-                        return false;
-                    }
-                case '>':
-                    if (!bracketsStack.empty() && bracketsStack.pop() == '<') {
-                        break;
-                    } else {
-                        return false;
-                    }
                 case ')':
-                    if (!bracketsStack.empty() && bracketsStack.pop() == '(') {
-                        break;
-                    } else {
-                        return false;
-                    }
                 case ']':
-                    if (!bracketsStack.empty() && bracketsStack.pop() == '[') {
-                        break;
-                    } else {
+                case '}':
+                    if (!(!bracketsStack.isEmpty() && isPaired(bracketsStack.pop(), bracket))) {
                         return false;
                     }
+                    break;
+                default: /* other character is invalid */
+                    return false;
             }
         }
-        return bracketsStack.empty();
+        return bracketsStack.isEmpty();
     }
 
-    /**
-     *
-     * @param args
-     * @TODO remove main method and Test using JUnit or other methodology
-     */
-    public static void main(String args[]) {
-        try (Scanner in = new Scanner(System.in)) {
-            System.out.println("Enter sequence of brackets: ");
-            String s = in.nextLine();
-            if (is_balanced(s)) {
-                System.out.println(s + " is balanced");
-            } else {
-                System.out.println(s + " ain't balanced");
-            }
-        }
+
+    public static void main(String[] args) {
+        assert isBalanced("[()]{}{[()()]()}");
+        assert !isBalanced("[(])");
     }
 }
