Brackets

src/main/java/codility/p07_stacks_and_queues/Brackets.java

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+package codility.p07_stacks_and_queues;
+
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/*
+https://app.codility.com/programmers/lessons/7-stacks_and_queues/brackets/
+ */
+public class Brackets {
+
+  public static final int INVALID_NESTING = 0;
+  public static final int PROPERLY_NESTING = 1;
+
+  private boolean isProperlyNested(char current, char popped) {
+    return ((popped == '(') && (current == ')')) ||
+        ((popped == '[') && (current == ']')) ||
+        ((popped == '{') && (current == '}'));
+  }
+
+  //https://app.codility.com/demo/results/training6VUEYT-SDD/
+  public int solution(String S) {
+    Deque<Character> stack = new ArrayDeque<Character>();
+    for (Character value : S.toCharArray()) {
+      switch (value) {
+        case '(':
+        case '[':
+        case '{': {
+          stack.push(value);
+          break;
+        }
+        case ')':
+        case ']':
+        case '}': {
+          if (stack.isEmpty()) {
+            return INVALID_NESTING;
+          }
+          Character popped = stack.pop();
+          if (!isProperlyNested(value, popped)) {
+            return INVALID_NESTING;
+          }
+        }
+
+      }
+    }
+    if (!stack.isEmpty()) {
+      return INVALID_NESTING;
+    }
+    return PROPERLY_NESTING;
+  }
+}

src/test/java/codility/p07_stacks_and_queues/BracketsTest.java

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+package codility.p07_stacks_and_queues;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static codility.p07_stacks_and_queues.Brackets.PROPERLY_NESTING;
+import static codility.p07_stacks_and_queues.Brackets.INVALID_NESTING;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class BracketsTest {
+
+  Brackets brackets;
+
+  @BeforeEach
+  public void init() {
+    brackets = new Brackets();
+  }
+
+  @Test
+  public void sample1() {
+    int solution = brackets.solution("{[()()]}");
+    assertThat(solution).isEqualTo(PROPERLY_NESTING);
+  }
+
+  @Test
+  public void sample2() {
+    int solution = brackets.solution("([)()]");
+    assertThat(solution).isEqualTo(INVALID_NESTING);
+  }
+
+
+}