Practice35 min
Practice: Counting & Canceling
XOR pair cancellation, popcount tricks, the bits(i>>1) DP, and positional bit reversal.
Single Number is the pure XOR fold; Number of 1 Bits wants the n & (n-1) loop; Counting Bits upgrades it to the shift-right DP; Reverse Bits drills the pull-low, push-left pump.