Letter Combinations of a Phone Number 解法
2017-12-13 17:30
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Letter Combinations of a Phone Number 解法
第11周题目难度:Media
LeetCode题号:17
题目
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.
Example1:
Input:Digit string “23”
Output: [“ad”, “ae”, “af”, “bd”, “be”, “bf”, “cd”, “ce”, “cf”].
思考
对每一个数字,我们添加他对应的几个字符这里维持一个vector,叫result用来保存每处理一个数字后的结果
当处理某个数字时,只用把result里面的每一个字符串分别加上该数字对应的那几个字符就行了
这里用了个temp的数组临时保存了每次处理后的结果
所以用swap函数交换temp和result
最后返回result就行了
注意开始如果数字串为空,相应的我们也要返回空
还有开始result要加入一个空的变量,是为了第一次循环可以顺利进行
代码
class Solution { public: vector<string> letterCombinations(string digits) { vector<string> result; static const vector<string> char_set = {"", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"}; if (digits.size() == 0) { return result; } result.push_back(""); for (int i = 0; i < digits.size(); i++) { int num = digits[i] - '0'; if (num < 0 || num > 9) { break; } string candidate = char_set[num]; vector<string> temp; for (int j = 0; j < candidate.size(); j++) { for (int k = 0; k < result.size(); k++) { temp.push_back(result[k] + candidate[j]); } } result.swap(temp); } return result; } };
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