sol.js

const input = ["ab", "aabbcc", "ababab", "abaabcca"];

const sol = (words) =>
  words.map(
    (word) =>
      word.split("").reduce(
        (prev, cur) =>
          prev.lastChar === cur
            ? {
                ...prev,
                lastChar: "",
                result: [...prev.result, `${prev.lastChar}${cur}`],
              }
            : { ...prev, lastChar: cur },
        {
          result: [],
          lastChar: "",
        }
      ).result.length
  );

console.log(sol(input));