(算法分析Week10)Letter Combinations of a Phone Number[Medium]
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17. Letter Combinations of a Phone Number[Medium]
题目来源
Description
Given a digit string, return all possible letter combinations that the number could represent.
A mapping of digit to letters (just like on the telephone buttons) is given below.
Input:Digit string "23"Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]
Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.
Solution
一个不停迭代的过程,粗暴一点就用嵌套循环,可以过。
用一个字符串数组存储结果,每次取接下来的那个数字,将其对应的字符,利用循环,分别接在原来的字符串数组后面即可。
数字对应字符串(键盘数字英文对应)也用一个字符串数组存储。
细心一点处理边界情况和空串。
Complexity analysis
O(nm)
n = digits.size
m = result.size
Code
class Solution {public: vector<string> letterCombinations(string digits) { vector<string> result; if (digits == "") //如果强行先push_back空串,当输入也为空时,则错误,所以要特殊处理 return result; result.push_back(""); //一开始没有注意这里,导致最内层循环无法进入 string tel[10] = {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}; for (int i = 0; i < digits.size(); i++) { string str = tel[digits[i] - '0']; vector<string> temp; for (int j = 0; j < str.size(); j++) { for (int k = 0; k < result.size(); k++) { temp.push_back(result[k] + str[j]); } } result = temp; } return result; }};
Result
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