Isomorphic Strings

Description

Given two strings s and t, determine if they are isomorphic.

Two strings are isomorphic if the characters in s can be replaced to get t.

All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.

Example 1:

Input: s = "egg", t = "add"
Output: true

Example 2:

Input: s = "foo", t = "bar"
Output: false

Example 3:

Input: s = "paper", t = "title"
Output: true

Note:
You may assume both s and t have the same length.

Solution(javascript)

/**
 * @param {string} s
 * @param {string} t
 * @return {boolean}
 */
const isIsomorphic = (s, t = '') => {
  const count = str => Array.prototype.reduce.call(str, (map, c, index) => {
    if (map[c]) {
      map[c].push(index)
    }
    map[c] = [index]
    return map
  }, {})
  const mapS = count(s)
  const mapT = count(t)

  for (let i = 0; i < s.length; i++) {
    const charS = s[i]
    const charT = t[i]
    for (let j = 0; j < mapS[charS].length; j++) {
      if (mapS[charS][j] !== mapT[charT][j]) {
        return false
      }
    }
  }
  return true
}