Count palindromic substrings

Question

A palindromic string reads the same backward as forward, such as 'madam'.

Now given a string, count how many substrings it has?

Like 'madam', it has following palindromic strings:

'm'
'a'
'd'
'a'
'm'
'ada'
'madam'

What is the time and space cost of your solution ? Could you improve it ?

Thanks to @TechieQian for helping with the test cases.

Code

/**
 * @param {string} str
 * @return {number}
 */
function countPalindromicSubstr(str) {
  // your code here
}

Source

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