力扣819、最常见的单词

1，for()拆分paragraph(4ms,87%;7.6MB,53%)

string mostCommonWord(string paragraph, vector<string>& banned) {
        unordered_set<string>Sbanned;
        for(string str:banned)
        Sbanned.insert(str);

        string str1;
        string str2;
        int max=0;
        unordered_map<string,int>ins;
        //注意最后一个单词直接截止了
        for(char ch:paragraph){
            //字母返回非0值
            if(isalpha(ch))
            //转为小写字母
            str1+=tolower(ch);

            else if(str1.size()>0){
                if(Sbanned.find(str1)==Sbanned.end())
                ++ins[str1];
                if(ins[str1]>max){
                max=ins[str1];
                str2=str1;
                }
                str1="";
            }
        }

        //为最后一个单词准备
        if(str1.size()>0){
                if(Sbanned.find(str1)==Sbanned.end())
                ++ins[str1];
                if(ins[str1]>max){
                max=ins[str1];
                str2=str1;
                }
                str1="";
            }
            return str2;

 

2,substr()截取paragraph(4ms,87%;7.6MB,53%)

string mostCommonWord(string paragraph, vector<string>& banned) {
        unordered_set<string>Sbanned(banned.begin(),banned.end());
        //转为小写
        for(char &ch:paragraph)
        ch=tolower(ch);

        int i=0;
        int max=0;
        string str1;
        unordered_map<string,int>ins;
        while(i<paragraph.size()){
            //字母返回非0
            if(isalpha(paragraph[i])){
                int j=i;
                i++;
                while(i<paragraph.size()&&isalpha(paragraph[i])) i++;
                //从j位开始截取i-j位
                string str=paragraph.substr(j,i-j);
                //计算str个数
                if(Sbanned.count(str)==0)
                ++ins[str];
                if(ins[str]>max){
                    max=ins[str];
                    str1=str;
                }
            }
            i++;
        }
        return str1;