Create 0316-remove-duplicate-letters.java

Author: sujal-goswami

java/0316-remove-duplicate-letters.java

@@ -0,0 +1,24 @@
+class Solution {
+    public String removeDuplicateLetters(String s) {
+        Set<Character> seen = new HashSet<>();
+        HashMap<Character, Integer> last = new HashMap<>();
+        for(char c : s.toCharArray()){
+            if(!last.containsKey(c))
+                last.put(c, s.lastIndexOf(c));
+        }
+        Stack<Character> stack = new Stack();
+        for(int i = 0; i < s.length(); i++){
+            char c = s.charAt(i);
+            if(seen.contains(c))
+                continue;
+            while(!stack.isEmpty() && stack.peek() > c && i < last.get(stack.peek()))
+                seen.remove(stack.pop());
+            stack.push(c);
+            seen.add(c);        
+        }
+        StringBuilder sb = new StringBuilder();
+        for(char c: stack)
+            sb.append(c);
+        return sb.toString();            
+    }
+}