leetcode 字元串

38.外觀數列

class Solution {
public:
    string countAndSay(int n) {
     string s = "1";//初始化第一個序列
     for(int i=1;i<n;i++)//循環n次
     {
         string ns = ""; //儲存臨時結果
         for(int j=0;j<s.size();)
         {
             int u = j;
             while(u < s.size()&&s[u]==s[j])u++;
             ns += to_string(u-j);
             ns += s[j];
             j=u;
         }
         s =ns;
     }    
     return s;
    }
};
           

49 字母異位詞

class Solution {
public:
    vector<vector<string>> groupAnagrams(vector<string>& strs) {
    unordered_map<string,vector<string>>hash;
    for(auto str:strs)
    {
        string key=str;
        sort(key.begin(),key.end());
        hash[key].push_back(str);
    }
    vector<vector<string>> res;
    for(auto item:hash) res.push_back(item.second);
    return res;
    }
};
           

151 reverse words in a string

class Solution {
public:
    string reverseWords(string s) {
        int k=0;
        for(int i=0;i<s.size();i++)
        {
            while(i<s.size()&&s[i]==' ')i++;
            if(i==s.size()) break;
            int j=i;
            while(j<s.size()&&s[j] !=' ')j++;
            reverse(s.begin()+i,s.begin()+j);
            if(k)s[k++]=' ';
            while(i<j)s[k++]=s[i++];
        }
        s.erase(s.begin()+k,s.end());
        reverse(s.begin(),s.end());
        return s;
    }
};