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17.电话号码的字母组合.js
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17.电话号码的字母组合.js
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/*
* @lc app=leetcode.cn id=17 lang=javascript
*
* [17] 电话号码的字母组合
*/
// @lc code=start
/**
* @param {string} digits
* @return {string[]}
*/
var letterCombinations = function (digits) {
if (!digits) return [];
const map = {
"2": "abc",
"3": "def",
"4": "ghi",
"5": "jkl",
"6": "mno",
"7": "qprs",
"8": "tuv",
"9": "wxyz"
};
if (digits.length === 1) return map[digits].split("");
let result = [];
// 方法一 递归
// const last = letterCombinations(digits.substring(1))
// let start = digits[0];
// for (let m = 0; m < map[start].length; m++) {
// for (let n = 0; n < last.length; n++) {
// result.push(map[start][m] + last[n])
// }
// }
// 方法二 回溯
const backtrack = (digits, combination) => {
if (!digits.length) {
result.push(combination);
} else {
const current = digits[0];
const letters = map[current];
for (let i = 0; i < letters.length; i++) {
backtrack(digits.substring(1), combination + letters[i])
}
}
}
backtrack(digits, "")
return result;
};
// @lc code=end