leetcode Letter Combinations of a Phone Number

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此题是非常经典的递归回溯法，

递归代码

class Solution {public:    vector<string> letterCombinations(string digits) {        vector<string> res;        string temp(digits.size(), ' ');        letterCombinationsHelper(digits, 0, temp, res);                return res;    } void letterCombinationsHelper(string &digits, int index, string &temp, vector<string> &res)    {        string nummap[] = {" ","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};                if(index==digits.size())        {            res.push_back(temp);            return ;        }                for(int i = 0; i < nummap[digits[index]-'0'].size(); ++i)        {            temp[index] = nummap[digits[index]-'0'][i];            letterCombinationsHelper(digits, index+1, temp, res);        }            }};

非递归运算

class Solution {public:    vector<string> letterCombinations(string digits) {        vector<string> res;                string nummap[] = {" ","","abc","def","ghi","jkl","mno","pqrs","tuv","wxyz"};                vector<int> indexNum(digits.size(), 0);                while(true)        {            string temp(digits.size(), ' ');            for(int i = 0; i < digits.size(); ++i)                temp[i] = nummap[digits[i]-'0'][indexNum[i]];                            res.push_back(temp);            int k = digits.size()-1;                        while(k>=0)            {                if(indexNum[k] < nummap[digits[k]-'0'].size()-1)                {                    indexNum[k]++;                    break;                }                else                {                    indexNum[k] = 0;                    k--;                }            }                        if(k<0)                break;                    }                return res;    }        };

参考http://www.cnblogs.com/TenosDoIt/p/3771254.html

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