Map the Letters in a String

Given a word, create an object that stores the indexes of each letter in an array.

• Make sure the letters are the keys.
• Make sure the letters are symbols.
• Make sure the indexes are stored in an array and those arrays are values.

Examples

mapLetters("dodo") ➞ { d: [0, 2], o: [1, 3] }

mapLetters("froggy") ➞ { f: [0], r: [1], o: [2], g: [3, 4], y: [5] }

mapLetters("grapes") ➞ { g: [0], r: [1], a: [2], p: [3], e: [4], s: [5] }

Notes

All strings given will be lowercase.