leetcode Letter Combinations of a Phone Number

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

评论
添加红包

请填写红包祝福语或标题

红包个数最小为10个

红包金额最低5元

当前余额3.43前往充值 >
需支付:10.00
成就一亿技术人!
领取后你会自动成为博主和红包主的粉丝 规则
hope_wisdom
发出的红包
实付
使用余额支付
点击重新获取
扫码支付
钱包余额 0

抵扣说明:

1.余额是钱包充值的虚拟货币,按照1:1的比例进行支付金额的抵扣。
2.余额无法直接购买下载,可以购买VIP、付费专栏及课程。

余额充值