# Maximum Product of Word Lengths

Given a string array `words`, find the maximum value of `length(word[i]) * length(word[j])` where the two words do not share common letters. You may assume that each word will contain only lower case letters. If no such two words exist, return 0.
Example 1:

```Input: `["abcw","baz","foo","bar","xtfn","abcdef"]`
Output: `16 Explanation: `The two words can be `"abcw", "xtfn"`.```

Example 2:

```Input: `["a","ab","abc","d","cd","bcd","abcd"]`
Output: `4 Explanation: `The two words can be `"ab", "cd"`.```

Example 3:

```Input: `["a","aa","aaa","aaaa"]`
Output: `0 Explanation: `No such pair of words.```

# Find All Numbers Disappeared in an Array

Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.
Find all the elements of [1, n] inclusive that do not appear in this array.
Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.
Example:

```Input:
[4,3,2,7,8,2,3,1]
Output:
[5,6]```

```seen = list()
result = list()
for item in nums:
if item in seen:
result += [item]
seen += [item]
else:
seen += [item]
return result```

```res = []
for x in nums:
if nums[abs(x) - 1] < 0:
res.append(abs(x))
else:
nums[abs(x) - 1] *= -1
return res```