题目:
题解:
class Solution {
public String removeDuplicateLetters(String s) {
boolean[] vis = new boolean[26];
int[] num = new int[26];
for (int i = 0; i < s.length(); i++) {
num[s.charAt(i) - 'a']++;
}
StringBuffer sb = new StringBuffer();
for (int i = 0; i < s.length(); i++) {
char ch = s.charAt(i);
if (!vis[ch - 'a']) {
while (sb.length() > 0 && sb.charAt(sb.length() - 1) > ch) {
if (num[sb.charAt(sb.length() - 1) - 'a'] > 0) {
vis[sb.charAt(sb.length() - 1) - 'a'] = false;
sb.deleteCharAt(sb.length() - 1);
} else {
break;
}
}
vis[ch - 'a'] = true;
sb.append(ch);
}
num[ch - 'a'] -= 1;
}
return sb.toString();
}
}