reverse_bits.cc

Author: jsgoller1

elements-of-programming-interviews/cpp/reverse_bits.cc

@@ -1,7 +1,25 @@
 #include "test_framework/generic_test.h"
+
+void printBin(unsigned long long val, size_t len, const std::string& suffix) {
+  std::string binval;
+  for (size_t i = 0; i < len; i++) {
+    binval.append(val & 1 ? "1" : "0");
+    val >>= 1;
+  }
+  reverse(binval.begin(), binval.end());
+  printf("%s (%s)\n", binval.c_str(), suffix.c_str());
+}
+
 unsigned long long ReverseBits(unsigned long long x) {
-  // TODO - you fill in here.
-  return 0;
+  unsigned long long y = x & 1;
+  for (int i = 0; i < (sizeof(x) * 8); i++) {
+    y <<= 1;
+    if (x & 1) {
+      y |= 1;
+    }
+    x >>= 1;
+  }
+  return y;
 }
 
 int main(int argc, char* argv[]) {
@@ -10,3 +28,6 @@ int main(int argc, char* argv[]) {
   return GenericTestMain(args, "reverse_bits.cc", "reverse_bits.tsv",
                          &ReverseBits, DefaultComparator{}, param_names);
 }
+
+// 0000101101000100011001000110101010111001000000000000000000000000
+// 000010110100010001100100011010101011100100000000000000000000000

elements-of-programming-interviews/problem_mapping.js

@@ -44,7 +44,7 @@ problem_mapping = {
         },
         "4.03 Reverse bits": {
             "C++: reverse_bits.cc": {
-                "passed": 0,
+                "passed": 10000,
                 "total": 10000
             },
             "Java: ReverseBits.java": {