老卫带你学---leetcode刷题(17. 电话号码的字母组合)

17. 电话号码的字母组合

问题：

给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。答案可以按 任意顺序 返回。

给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。

示例 1：

输入：digits = "23"
输出：["ad","ae","af","bd","be","bf","cd","ce","cf"]
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示例 2：

输入：digits = ""
输出：[]
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示例 3：

输入：digits = "2"
输出：["a","b","c"]
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提示：

0 <= digits.length <= 4
digits[i] 是范围 ['2', '9'] 的一个数字。
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解决：

递归搜索

var result []string

var phone = map[string][]string{
	"2":[]string{"a","b","c"},
	"3":[]string{"d","e","f"},
	"4":[]string{"g","h","i"},
	"5":[]string{"j","k","l"},
	"6":[]string{"m","n","o"},
	"7":[]string{"p","q","r","s"},
	"8":[]string{"t","u","v"},
	"9":[]string{"w","x","y","z"},
}

func letterCombinations(digits string) []string {
	result = []string{}
	if len(digits)==0{
		return []string{}
	}
	helper("",digits)
	return result
}

func helper(s,next string){
	if len(next)==0{
		result = append(result, s)
	} else{
		for _,j := range phone[string(next[0])]{
			helper(s+j,next[1:])
		}
	}
}
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