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[LeetCode 解題] 17. Letter Combinations of a Phone Number | 想清楚 depth 的意義
題目連結：17. Letter Combinations of a Phone Number 我覺得這種 backtracking 或是 dfs 的題目都需要想清處 depth 的定義是什麼，想清楚就會好寫許多。 程式實做 class Solution { public: vector<string> letterCombinations(string digits) { if (digits.size() == 0) return {}; vector<string> phoneNumber = { "", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz" }; vector<string> combs; string current; backtracking(0, digits, current, phoneNumber, combs); return combs; } void backtracking(int index, string digits, string current, vector<string> phoneNumber, vector<string> &combs) { if (index >= digits.size()) { combs.push_back(current); return; } int i = digits[index] - '0'; for (char c : phoneNumber[i]) { current.push_back(c); backtracking(index + 1, digits, current, phoneNumber, combs); current.pop_back(); } } };