find arrray element

for num in nums:
	if nums[abs(num)-1]>0: #not visited
		nums[abs(num)-1] = -nums[abs(num)-1] #why the -1? because the array starts from 0
res = []
for i in range(len(nums)):
	if nums[i]>0:
		res.append(i+1) #unvisited num
return res