LeetCode 316. Remove Duplicate Letters（贪心）

class Solution {
public:
    int vis[30];
    int m[30];
    string ans;
    int res;
    int b=-1;
    string removeDuplicateLetters(string s) {

        if(s=="")
            return "";
        memset(vis,0,sizeof(vis));
        int pos = 0;
        while(1)
        {
            pos = fun(s,pos);
            ans+=(res+'a');
            vis[res]=1;
            if(ans.length()==b)
                break;
        }

        return ans;

    }

    int fun(string s,int pos)
    {
        memset(m,0,sizeof(m));

        int x=0;
        res = 31;
        int j=-2;
        for(int i=s.length()-1;i>=pos;i--)
        {
            if(vis[s[i]-'a']==1)
                continue;
            if(m[s[i]-'a']==0)
            {
                x++;
                m[s[i]-'a']=1;
                res = s[i]-'a';
                j=i;
            }
            else
            {
                if(res>=s[i]-'a')
                {
                    res=s[i]-'a';
                    j=i;
                }
            }
        }
        
        if(b == -1)
            b=x;

        return j+1;
    }
};