[数据结构与算法]leetcode哈希表(python与c++)

1.整数转罗马数字

python:

class Solution:
    def intToRoman(self, num: int) -> str:
        dict_ = {1000:'M', 900:'CM', 500:'D', 400:'CD', 100:'C', 90:'XC', 50:'L', 40:'XL', 10:'X', 9:'IX', 5:'V', 4:'IV', 1:'I'}
        res = ''
        for key in dict_:
            count = num // key
            res += count * dict_[key]
            num %= key
        return res

c++:?

class Solution {
public:
    string intToRoman(int num) {
        int value[] = {1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1};
        string str_[] = {"M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I"};
        string res;
        for(int i = 0; i < 13; i++){
            while(num >= value[i]){
                num -= value[i];
                res += str_[i];
            }
        }
        return res;
    }
};

2.电话号码的字母组合?

?python:

class Solution:
    def help(self, digits, track):
        if len(digits)==0:
            self.res.append(''.join(track))
            return
        for letter in self.dict_[digits[0]]:
            # store = track.copy()
            track.append(letter)
            self.help(digits[1:], track)
            # track.pop()
            track = store
    def letterCombinations(self, digits: str) -> List[str]:
        if len(digits)==0:
            return []
        self.dict_={"2":"abc","3":"def","4":"ghi","5":"jkl","6":"mno","7":"pqrs","8":"tuv","9":"wxyz"}
        self.res = []
        self.help(digits, [])
        return self.res

c++:

class Solution {
public:
    vector<string> res;
    // unordered_map<char, string> phoneMap;
    void help(string digits, vector<char> track, unordered_map<char, string> phoneMap){
        if(digits.empty()){
            string str(track.begin(), track.end());
            res.push_back(str);
        }
        for(int i=0; i < phoneMap[digits[0]].size(); i++){
            track.push_back(phoneMap[digits[0]][i]);
            help(digits.substr(1, digits.size() - 1), track, phoneMap);
            track.pop_back();
        }
    }
    vector<string> letterCombinations(string digits) {
        if (digits.empty()) {
            return res;
        }
        unordered_map<char, string> phoneMap{
            {'2', "abc"},
            {'3', "def"},
            {'4', "ghi"},
            {'5', "jkl"},
            {'6', "mno"},
            {'7', "pqrs"},
            {'8', "tuv"},
            {'9', "wxyz"}
        };
        vector<char> track;
        help(digits, track, phoneMap);
        return res;

    }
};