Follow https://discuss.leetcode.com/topic/65738/java-accepted-simple-solution

```
def find_disappeared_numbers(nums)
for i in 0..nums.length-1
index = nums[i].abs() - 1
nums[index] = -nums[index].abs() if nums[index] > 0
end
result = []
for i in 0..nums.length-1
result << i+1 if nums[i] > 0
end
result
end
```