TwoSum | Expected: [0, 1], instead got: [0, 0] | Ruby indexs' problem

Question

def two_sum(nums, tg)
  b = []
  nums.sort.combination(2){|x| b << x}
  c = b.reject{|x| x.sum != tg}[0]
  [nums.index(c[0]), nums.index(c[1])]
end

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