input = [5, 6, 3, 4, 3, 6, 4]
repeated_nums = {}
min_idx = input.size
input.each.with_index do |num, idx|
prev_idx = repeated_nums[num]
repeated_nums[num] = idx
if prev_idx and min_idx > prev_idx
min_idx = prev_idx
end
end
raise 'Input does not contain duplicates.' if min_idx == input.size
puts min_idx
aW5wdXQgPSBbNSwgNiwgMywgNCwgMywgNiwgNF0KcmVwZWF0ZWRfbnVtcyA9IHt9Cm1pbl9pZHggPSBpbnB1dC5zaXplCgppbnB1dC5lYWNoLndpdGhfaW5kZXggZG8gfG51bSwgaWR4fAogIHByZXZfaWR4ID0gcmVwZWF0ZWRfbnVtc1tudW1dIAogIHJlcGVhdGVkX251bXNbbnVtXSA9IGlkeAogIGlmIHByZXZfaWR4IGFuZCBtaW5faWR4ID4gcHJldl9pZHgKICAgIG1pbl9pZHggPSBwcmV2X2lkeAogIGVuZAplbmQKcmFpc2UgJ0lucHV0IGRvZXMgbm90IGNvbnRhaW4gZHVwbGljYXRlcy4nIGlmIG1pbl9pZHggPT0gaW5wdXQuc2l6ZQpwdXRzIG1pbl9pZHggCg==