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// @Title: 电话号码的字母组合 (Letter Combinations of a Phone Number)
// @Author: 15816537946@163.com
// @Date: 2020-06-25 07:15:36
// @Runtime: 4 ms
// @Memory: 2.6 MB
import "fmt"

/*
 * @lc app=leetcode.cn id=17 lang=golang
 *
 * [17] 电话号码的字母组合
 *
 * https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/description/
 *
 * algorithms
 * Medium (50.95%)
 * Likes:    450
 * Dislikes: 0
 * Total Accepted:    46.7K
 * Total Submissions: 91.8K
 * Testcase Example:  ""23""
 *
 * 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。
 *
 * 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:
 *
 * 输入:"23"
 * 输出:["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
 *
 *
 * 说明:
 * 尽管上面的答案是按字典序排列的,但是你可以任意选择答案输出的顺序。
 *
 */
func letterCombinations(digits string) []string {
	if len(digits) == 0 {
		return nil
	}

	phoneMap := map[int][]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",
		},
	}

	ans := make([]string, 0)
	var backtrack func(string, []byte)
	backtrack = func(out string, idx []byte) {
		fmt.Println("idx ->", idx)
		// if len(idx) == 0 {
		if len(idx) == 0 {
			fmt.Println("out ->", out)
			tmp := out
			ans = append(ans, tmp)
			return
		}
		fmt.Println("debug ->", 1)
		for _, letters := range phoneMap[int(idx[0]-'0')] {
			for _, letter := range letters {
				backtrack(out+string(letter), idx[1:])
			}
		}
		fmt.Println("debug ->", 2)
	}

	backtrack("", []byte(digits))
	return ans
}