count set bits from -n to n : done

Author: Ram swaroop

src/me/ramswaroop/bits/CountSetBitsFromMinusNtoN.java

@@ -0,0 +1,38 @@
+package me.ramswaroop.bits;
+
+/**
+ * Created by IntelliJ IDEA.
+ *
+ * @author: ramswaroop
+ * @date: 7/22/15
+ * @time: 12:42 PM
+ */
+public class CountSetBitsFromMinusNtoN {
+
+    /**
+     * Explanation:
+     *
+     * -3:  101
+     * -2:  110
+     * -1:  111
+     * 0:   000
+     * 1:   001
+     * 2:   010
+     * 3:   110
+     *
+     * If you fold the above representation between -1 and 0, the total no. of set bits from -3 to 2
+     * will be equal to the total no. of bits in nos. from -3 to 2.
+     *
+     * @param n
+     * @return
+     */
+    public static int countSetBitsFromMinusNtoN(int n) {
+        return n * 32 + CountSetBits.countSetBits((long) n); // 32 because int is of 32 bits in java
+    }
+
+    public static void main(String a[]) {
+        System.out.println(countSetBitsFromMinusNtoN(3));
+        System.out.println(countSetBitsFromMinusNtoN(0));
+        System.out.println(countSetBitsFromMinusNtoN(9));
+    }
+}