ABC121D

D - XOR World

• 
• Thoughts.
  • If you think about each bit individually, you can figure out the number of 1’s in the interval by the remainder of the power of 2, right?
• Official Explanation
  • It is a logarithmic order solution
  • Constant order if you notice the following
  • $f(A,B)=f(0,A-1)\oplus f(0,B)$ - Arbitrary interval is the difference between intervals from 0
  • $2n\oplus (2n+1)=1$ - XOR of an even number and the next odd number is 1

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