每日一题 --- 17. 电话号码的字母组合[力扣][Go]

// 回溯法,深度优先算法 官方题解
var phoneMap = map[uint8]string{
    50: "abc",
    51: "def",
    52: "ghi",
    53: "jkl",
    54: "mno",
    55: "pqrs",
    56: "tuv",
    57: "wxyz",
}
var combinations []string
func letterCombinations(digits string) []string {
    if len(digits) == 0 {
        return []string{}
    }
    combinations = []string{}
    backtrack(digits, 0, "")
    return combinations
}
func backtrack(digits string, index int, combination string) {
    if index == len(digits) {
        combinations = append(combinations, combination)
    } else {
        digit := digits[index]
        letters := phoneMap[digit]
        lettersCount := len(letters)
        for i := 0; i < lettersCount; i++ {
            backtrack(digits, index + 1, combination + string(letters[i]))
        }
    }
}