Binary Reversal

ardallie · ardallie · commit 03cd25c78640 · 2021-08-11T23:11:27.000+01:00
diff --git a/src/easy/BinaryReversal.java b/src/easy/BinaryReversal.java
@@ -0,0 +1,58 @@
+package easy;
+
+/**
+ * Have the function BinaryReversal(str) take the str parameter being passed,
+ * which will be a positive integer, take its binary representation
+ * (padded to the nearest N * 8 bits), reverse that string of bits,
+ * and then finally return the new reversed string in decimal form.
+ * ---
+ * For example: if str is "47" then the binary version of this integer is 101111,
+ * but we pad it to be 00101111. Your program should reverse this binary string
+ * which then becomes: 11110100 and then finally return
+ * the decimal version of this string, which is 244.
+ */
+public class BinaryReversal {
+
+  /**
+   * Left pad the string with zeroes,
+   * e.g. padLeft("fade", 8) -> "0000fade"
+   *
+   * @param str string to be padded
+   * @param len new fixed length after applying the padding
+   * @return padded string (e.g. 000000xxx)
+   */
+  private static String padLeft(String str, int len) {
+    return String.format("%" + len + "s", str).replace(" ", "0");
+  }
+
+  /**
+   * Binary Reversal function.
+   *
+   * @param str input string
+   * @return the decimal version of this string
+   */
+  private static int binaryReversal(String str) {
+    String binStr = Integer.toBinaryString(Integer.parseInt(str));
+    int add = binStr.length() % 8 == 0 ? 0 : 1;
+    int pad = add + binStr.length() / 8;
+    String padStr = padLeft(binStr, pad * 8);
+    StringBuilder result = new StringBuilder();
+    for (int i = padStr.length() - 1; i >= 0; i--) {
+      result.append(Character.getNumericValue(padStr.charAt(i)));
+    }
+    return Integer.parseInt(result.toString(), 2);
+  }
+
+  /**
+   * Entry point.
+   *
+   * @param args command line arguments
+   */
+  public static void main(String[] args) {
+    var result1 = binaryReversal("47");
+    System.out.println(result1);
+    var result2 = binaryReversal("2");
+    System.out.println(result2);
+  }
+
+}
