Map the Letters in a String

Given a word, create a dictionary that stores the indexes of each letter in a list.

• Make sure the letters are the keys.
• Make sure the letters are symbols.
• Make sure the indexes are stored in a list and those lists are values.

Examples

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

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

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

Notes

All strings given will be lowercase.