When I've grown sweet potatoes, I found that the underground growth (the roots and the potatoes themselves) as well as the above-ground vines can get pretty extensive. Sweet potatoes would choke out the corn (even though corn has a pretty shallow root system), so I personally wouldn't plant them in between each other. You could certainly plant them next to each other with about 3-4 feet of growing space around the potatoes with no issues. You'll also want some space between the sweet potatoes so that you can harvest them easily.
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