solves binary watch

Author: anishLearnsToCode

src/BinaryWatch.java

@@ -0,0 +1,39 @@
+import java.util.ArrayList;
+import java.util.List;
+
+public class BinaryWatch {
+    public List<String> readBinaryWatch(int num) {
+        List<String> result = new ArrayList<String>();
+
+        for(int i = 0 ; i < 12 ; i++){
+            for(int j=0 ; j < 60 ; j++){
+                int total = countDigits(i) + countDigits(j);
+                if(total == num){
+                    StringBuilder time = new StringBuilder();
+                    time.append(i)
+                            .append(":")
+                            .append(j < 10 ? 0 : "")
+                            .append(j);
+
+                    result.add(time.toString());
+                }
+            }
+        }
+
+        return result;
+    }
+
+    public int countDigits(int num){
+        int result = 0;
+
+        while(num > 0){
+            if((num & 1) == 1){
+                result++;
+            }
+
+            num >>= 1;
+        }
+
+        return result;
+    }
+}