Find Common Characters

Description

Given an array A of strings made only from lowercase letters, return a list of all characters that show up in all strings within the list (including duplicates).  For example, if a character occurs 3 times in all strings but not 4 times, you need to include that character three times in the final answer.

You may return the answer in any order.

 

Example 1:

Input: ["bella","label","roller"]
Output: ["e","l","l"]

Example 2:

Input: ["cool","lock","cook"]
Output: ["c","o"]

 

Note:

1. 1 <= A.length <= 100
2. 1 <= A[i].length <= 100
3. A[i][j] is a lowercase letter

Solution(javascript)

/**
 * 最后的结果其实是一个累积的结果
 * @param {string[]} A
 * @return {string[]}
 */
const commonChars = function (A = []) {
  let prev = null
  A.forEach((str) => {
    const next = {}
    for (const c of str) {
      if (!prev) {
        next[c] = (next[c] || 0) + 1
      } else if (prev[c]) {
        prev[c] -= 1
        next[c] = (next[c] || 0) + 1
      }
    }
    prev = next
  })
  return Object.keys(prev).reduce((acc, c) => {
    for (let i = 0; i < prev[c]; i++) {
      acc.push(c)
    }
    return acc
  }, [])
}