Create binary-watch.cpp

Author: kamyu104

C++/binary-watch.cpp

@@ -0,0 +1,28 @@
+// Time:  O(1)
+// Space: O(1)
+
+class Solution {
+public:
+    vector<string> readBinaryWatch(int num) {
+        vector<string> result;
+        for (int h = 0; h < 12; ++h) {
+            for (int m = 0; m < 60; ++m) {
+                if (bit_count(h) + bit_count(m) == num) {
+                    const auto hour = to_string(h);
+                    const auto minute = m < 10 ? "0" + to_string(m) : to_string(m);
+                    result.emplace_back(hour + ":" + minute);
+                }
+            }
+        }
+        return result;
+    }
+
+private:
+    int bit_count(int bits) {
+        int count = 0;
+        for (; bits; bits &= bits - 1) {
+            ++count;
+        }
+        return count;
+    }
+};