Add solution of SimplifyPath task

Author: andrei-punko

src/main/java/by/andd3dfx/collections/SimplifyPath.java

@@ -0,0 +1,100 @@
+package by.andd3dfx.collections;
+
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Deque;
+import java.util.List;
+
+/**
+ * <pre>
+ * <a href="https://leetcode.com/problems/simplify-path/description/">Task description</a>
+ *
+ * You are given an absolute path for a Unix-style file system, which always begins with a slash '/'. Your task is to transform this absolute path into its simplified canonical path.
+ *
+ * The rules of a Unix-style file system are as follows:
+ *
+ *     A single period '.' represents the current directory.
+ *     A double period '..' represents the previous/parent directory.
+ *     Multiple consecutive slashes such as '//' and '///' are treated as a single slash '/'.
+ *     Any sequence of periods that does not match the rules above should be treated as a valid directory or file name. For example, '...' and '....' are valid directory or file names.
+ *
+ * The simplified canonical path should follow these rules:
+ *
+ *     The path must start with a single slash '/'.
+ *     Directories within the path must be separated by exactly one slash '/'.
+ *     The path must not end with a slash '/', unless it is the root directory.
+ *     The path must not have any single or double periods ('.' and '..') used to denote current or parent directories.
+ *
+ * Return the simplified canonical path.
+ *
+ * Example 1:
+ * Input: path = "/home/"
+ * Output: "/home"
+ * Explanation:
+ * The trailing slash should be removed.
+ *
+ * Example 2:
+ * Input: path = "/home//foo/"
+ * Output: "/home/foo"
+ * Explanation:
+ * Multiple consecutive slashes are replaced by a single one.
+ *
+ * Example 3:
+ * Input: path = "/home/user/Documents/../Pictures"
+ * Output: "/home/user/Pictures"
+ * Explanation:
+ * A double period ".." refers to the directory up a level (the parent directory).
+ *
+ * Example 4:
+ * Input: path = "/../"
+ * Output: "/"
+ * Explanation:
+ * Going one level up from the root directory is not possible.
+ *
+ * Example 5:
+ * Input: path = "/.../a/../b/c/../d/./"
+ * Output: "/.../b/d"
+ * Explanation:
+ * "..." is a valid name for a directory in this problem.
+ * </pre>
+ */
+public class SimplifyPath {
+
+    public static String simplifyPath(String path) {
+        Deque<String> stack = new ArrayDeque<>();
+
+        path = path.replaceAll("/+", "/");
+        StringBuilder accumulator = new StringBuilder();
+        var chars = path.toCharArray();
+        var i = 1;
+        while (i < chars.length) {
+            switch (chars[i]) {
+                case '/':
+                    if (accumulator.toString().equals("..") && !stack.isEmpty()) {
+                        stack.pop();
+                    } else {
+                        checkAndPush(stack, accumulator);
+                    }
+                    accumulator = new StringBuilder();
+                    break;
+
+                default:
+                    accumulator.append(chars[i]);
+            }
+            i++;
+        }
+        checkAndPush(stack, accumulator);
+
+        List<String> folders = Arrays.stream(stack.toArray(new String[0]))
+            .toList()
+            .reversed();
+        return "/" + String.join("/", folders);
+    }
+
+    private static void checkAndPush(Deque<String> stack, StringBuilder accumulator) {
+        var string = accumulator.toString();
+        if (!string.isEmpty() && !string.matches("\\.{1,2}")) {
+            stack.push(string);
+        }
+    }
+}

src/test/java/by/andd3dfx/collections/SimplifyPathTest.java

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+package by.andd3dfx.collections;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.Test;
+
+public class SimplifyPathTest {
+
+    @Test
+    public void testSimplifyPath() {
+        assertThat(SimplifyPath.simplifyPath("/home/")).isEqualTo("/home");
+        assertThat(SimplifyPath.simplifyPath("/home//foo/")).isEqualTo("/home/foo");
+        assertThat(SimplifyPath.simplifyPath("/home/user/Documents/../Pictures"))
+            .isEqualTo("/home/user/Pictures");
+        assertThat(SimplifyPath.simplifyPath("/../")).isEqualTo("/");
+        assertThat(SimplifyPath.simplifyPath("/.../a/../b/c/../d/./"))
+            .isEqualTo("/.../b/d");
+    }
+}