LeetCode开心刷题第九天——17Letter Combinations of a Phone Number

Given a string containing digits from 2-9 inclusive, 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. Note that 1 does not map to any letters.

Example:

Input: "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

Special Point:
C11 is an effective tool.From now on I need to get familiar with C11.
Some usage in for loop need to be declare:

1.All These instance only want to declare one thing:
if you want to change value during C11 for loop,you need to use atuo&
Source of theory:
https://blog.csdn.net/hailong0715/article/details/54172848

    std::vector<int> vec {1,2,3,4,5,6,7,8,9,10};
    cout << "修改前" << endl;
    for (auto n :vec)
        std::cout << n++;
 
    cout << endl;
    cout << "修改后" << endl;
    for (auto j : vec)
        std::cout << j;

修改前
12345678910
修改后
12345678910

    std::vector<int> vec {1,2,3,4,5,6,7,8,9,10};
    cout << "修改前" << endl;
    for (auto& n :vec)
        std::cout << n++;
 
    cout << endl;
    cout << "修改后" << endl;
    for (auto j : vec)
        std::cout << j;

修改前
12345678910
修改后
234567891011