Buttercola: Leetcode: Palindrome Permutation

Buttercola: Leetcode: Palindrome Permutation

Leetcode: Palindrome Permutation

Given a string, determine if a permutation of the string could form a palindrome.

For example,
"code" -> False, "aab" -> True, "carerac" -> True.

Understand the problem:
The problem can be easily solved by count the frequency of each character using a hash map. The only thing need to take special care is consider the length of the string to be even or odd. 
  -- If the length is even. Each character should appear exactly times of 2, e.g. 2, 4, 6, etc..
  -- If the length is odd. One and only one character could appear odd times. 

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