Letter Combinations of a Phone Number

目录

• 题目链接
• 注意点
• 解法
• 小结

题目链接

Letter Combinations of a Phone Number - LeetCode

注意点

• 可以不用按字典序排序

解法

解法一：输入的数字逐个处理，在已经生成的字符串后面追加该当前数字对应的所有字符。时间复杂度为O(n)

class Solution {
public:
    vector<string> letterCombinations(string digits) {
        vector<string> ans,temp_ans;
        map<char,vector<string>> mp;
        mp['2']={"a","b","c"};
        mp['3']={"d","e","f"};
        mp['4']={"g","h","i"};
        mp['5']={"j","k","l"};
        mp['6']={"m","n","o"};
        mp['7']={"p","q","r","s"};
        mp['8']={"t","u","v"};
        mp['9']={"w","x","y","z"};
        int i,j,k,n = digits.length();
        for(i = 0;i < n;i++)
        {
            int size = ans.size();
            vector<string> v = mp[digits[i]];
            for(j = 0;j < v.size();j++)
            {
                for(k = 0;k < size;k++)
                {
                    string temp=ans[k]+v[j];
                    temp_ans.push_back(temp);
                }
                if(size==0) temp_ans.push_back(v[j]);
            }
            swap(ans,temp_ans);
            temp_ans.clear();
        }
        return ans;
    }
};

小结

• 代码网上看来的，自己重新打了一遍。相比其他博客，这个算是最好理解的。