Convert weights into cumulative ranges. If weights = [1, 3, 2], total weight = 6.
Ranges: index 0 covers [0, 1), index 1 covers [1, 4), index 2 covers [4, 6).
Pick a random number r in [0, 6). Find which range r falls into using binary search.
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(Convert weights to ranges)
Convert weights into cumulative ranges. If weights = [1, 3, 2], total weight = 6.
Ranges: index 0 covers [0, 1), index 1 covers [1, 4), index 2 covers [4, 6).
Pick a random number r in [0, 6). Find which range r falls into using binary search.