LeetCode Letter Combinations of a Phone Number

题目

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.

将每个数字模拟为一位，进制为这个数字可以代表的字母数量，模拟累加过程即可。

代码：

string dic[10]={"","abc","def","ghi","jkl","mon","pqrs","tuv","wxyz"};

class Solution {
public:
vector<string> letterCombinations(string digits) {
int size=digits.size();
vector<string> ans;
string s;
int *flag=new int [size];	//记录相应标号数字取到对应的字符的编号
int i;
for(i=0;i<size;i++)
flag[i]=0;
while(i>=0)
{
s.clear();
for(i=0;i<size;i++)
s.push_back(dic[digits[i]-'1'][flag[i]]);
ans.push_back(s);
i=size-1;
while(i>=0&&flag[i]+1>=dic[digits[i]-'1'].size())
flag[i--]=0;
if(i>=0)
flag[i]++;
}
delete [] flag;
return ans;
}
};