1081. Smallest Subsequence of Distinct Characters
Medium
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Return the lexicographically smallest subsequence of text
that contains all the distinct characters of text
exactly once.
Example 1:
Input: "cdadabcc" Output: "adbc"
Example 2:
Input: "abcd" Output: "abcd"
Example 3:
Input: "ecbacba" Output: "eacb"
Example 4:
Input: "leetcode" Output: "letcod"
Note:
-
1 <= text.length <= 1000
-
text
consists of lowercase English letters.
string smallestSubsequence(string text){
stack<char> s;
unordered_map<char,int> Map;
unordered_set<char> Visited;
string Result;
for(int i = 0;i < text.length();i++){
Map[text[i]] ++;
}
for(int i = 0;i < text.length();i ++){
Map[text[i]] --;
if(Visited.find(text[i]) != Visited.end()){
continue;
}
while(!s.empty() && text[i] < s.top() && Map[s.top()] > 0){//--case : 1 要保证字符串中所有字符都包含在结果里,必须加入条件Map[s.top()]>0
//--case : 2 如果不用保证最后的结果必须包含所有字符,就把这个条件删掉
Visited.erase(s.top());
s.pop();
}
s.push(text[i]);
Visited.insert(text[i]);
}
while(!s.empty()){
Result += s.top();
s.pop();
}
reverse(Result.begin(),Result.end());
return Result;
}