// Runtime: 68 ms, faster than 87.18% of JavaScript online submissions for Letter Case Permutation.
// Memory Usage: 37.3 MB, less than 100.00% of JavaScript online submissions for Letter Case Permutation.

var letterCasePermutation = function(inputString) {
    const getNewStringsByAddingUpLowChar = (strings, char) => {
        let variants = []
        if (!strings.length) {
            if (!isNaN(char)) {
                return [char]
            }
            return [char.toUpperCase(), char.toLowerCase()]
        }
        strings.forEach(item => {
            if (!isNaN(char)) {
                variants.push(item + char)
                return
            }
            variants.push(item + char.toUpperCase())
            variants.push(item + char.toLowerCase())
        })
        return variants
    }

    let result = []
    inputString.split('').forEach(char => {
        result = getNewStringsByAddingUpLowChar(result, char)
    })
    return result
};