int main(void){
char s[100];
while(gets(s)){
char *res=removeDuplicateLetters(s);
printf("%s输出的结果为：",s);
puts(res);
}
return 0;
}
string removeDuplicateLetters(string s) {
// Greddy
// Each time we select a character which has the smllest lexicographical order from left to right util we meet a non
// -duplicate character which we cannot skip
// Notice :
// when we meet a non-duplicate character, this means that we must select a character from the substring (s[0] .... s[pos])
// which consists of character from beginning of the string s to the position of the non-duplicate character
// The non-duplicate character has two kinds:
// 1. it only appear once among the whole string s
// 2. it appears many times, but we have met all of the duplicate position, this position is its last appearance
// so we should maintain characters' count of appearance.
// Once we have selected a characer we must delete all same character after its position
// find next character from the substring
if(s.empty())
return "";
vector<int> cnts(26, 0);
for(auto c : s)
cnts[c-'a']++;
// the position of the character we will select
int pos = 0;
for(int i = 0; i < s.length(); i++){
// Select the smallest lexicographical order character among the duplicate characters
if(s[i] < s[pos])
pos = i;
// update the cnts infomation of the chatacter we meet,
// if s[i] is non-duplicate, we select a character(s[pos]) immediately
// pos is in [0...i]
if(--cnts[s[i]-'a'] == 0)
break;
}
cout <<pos << endl;
char selected = s[pos];
string sub_s;
// delete all selected character after position of pos
for(int i = pos+1; i < s.length(); i++)
if(s[i] != selected)
sub_s += s[i];
// find next character form the substring
string ret = selected + removeDuplicateLetters(sub_s);
return ret;
}
string removeDuplicateLetters(string s) {
array<int, 26> counts;
counts.fill(0);
for (char c : s)
counts[c-'a']++;
int pos = 0;
for (int i = 0; i != s.size(); i++) {
if (s[i] < s[pos])
pos = i;
if (--counts[s[i]-'a'] == 0)
break;
}
if (s.empty())
return "";
string substr = s.substr(pos+1);
substr.erase(std::remove(substr.begin(), substr.end(), s[pos]), substr.end());
return s[pos] + removeDuplicateLetters(substr);
}
int main() {
string s = "rusrbofeggbbkyuyjsrzornpdguwzizqszpbicdquakqws";
cout<<removeDuplicateLetters(s)<<endl;
return 0;
}
