Unique substrings in circular string in JavaScript

Problem

Suppose we have a S, str. which is an infinite wraparound string of the string −

"abcdefghijklmnopqrstuvwxyz".

Therefore, S will look like this −

"...zabcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyzabcd....".

We are required to write a JavaScript function that takes in str, let’s call that string str, as the only argument.

• Our function should find out how many unique non-empty substrings of str are present in S.

• Our function should finally return the number of different non-empty substrings of str in the string S.

For example, if the input to the function is −

const str = "zab";

Then the output should be −

const output = 6;

Output Explanation

There are six substrings "z", "a", "b", "za", "ab", "zab" of string "zab" in the string S.

Example

The code for this will be −

const str = "zab";
const allSubstrings = (str = '') => {
   const dp = new Array(26).fill(0);
   dp[str.charCodeAt(0) - 97] = 1;
   maxCount = 1;
   for (let i = 1; i < str.length; i++) {
      if ((str.charCodeAt(i) - str.charCodeAt(i - 1) == 1) || (str.charCodeAt(i) - str.charCodeAt(i - 1) == -25)) {
         maxCount++;
      } else {
         maxCount = 1;
      }
      dp[str.charCodeAt(i) - 97] = Math.max(dp[str.charCodeAt(i) - 97], maxCount);
   }
   return dp.reduce((item, val) => {
      return val + item;
   })
};
console.log(allSubstrings(str));

Output

And the output in the console will be −

6