fix EmptyStackException

realDuYuanChao · realDuYuanChao · commit dff1b0931c0c · 2019-09-25T08:57:42.000+08:00
diff --git a/DataStructures/Stacks/BalancedBrackets.java b/DataStructures/Stacks/BalancedBrackets.java
@@ -38,29 +38,25 @@ static boolean is_balanced(String s) {
                     bracketsStack.push(x);
                     break;
                 case '}':
-                    if (bracketsStack.peek() == '{') {
-                        bracketsStack.pop();
+                    if (!bracketsStack.empty() && bracketsStack.pop() == '{') {
                         break;
                     } else {
                         return false;
                     }
                 case '>':
-                    if (bracketsStack.peek() == '<') {
-                        bracketsStack.pop();
+                    if (!bracketsStack.empty() && bracketsStack.pop() == '<') {
                         break;
                     } else {
                         return false;
                     }
                 case ')':
-                    if (bracketsStack.peek() == '(') {
-                        bracketsStack.pop();
+                    if (!bracketsStack.empty() && bracketsStack.pop() == '(') {
                         break;
                     } else {
                         return false;
                     }
                 case ']':
-                    if (bracketsStack.peek() == '[') {
-                        bracketsStack.pop();
+                    if (!bracketsStack.empty() && bracketsStack.pop() == '[') {
                         break;
                     } else {
                         return false;
