17. Letter Combinations of a Phone Number

这是一个队列的经典例子！

原题

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”].

Example1：

Input: “12”
Output: “1a” “1b” “1c”

代码实现

        public List<string> LetterCombinations(string digits)
        {
            if (digits.Trim() == string.Empty) return new List<string>();
            Queue<string> q = new Queue<string>();
            string[] mapping = { "0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz" };
            q.Enqueue("");
            for (int i = 0; i < digits.Length; i++)
            {
                int x = digits[i] - 48;
                while (q.Peek().Length == i)
                {
                    string t = q.Dequeue();
                    foreach (var ch in mapping[x])
                    {
                        q.Enqueue(t + ch);
                    }
                }
            }
            return q.ToList();
        }

结果模拟

Input: “234”

结果：

绿色的为最后留在队列中的List。

题库

Leetcode算法题目解决方案每天更新在github库中，欢迎感兴趣的朋友加入进来，也欢迎star，或pull request。https://github.com/jackzhenguo/leetcode-csharp

完成题目索引

http://blog.csdn.net/daigualu/article/details/73008186