feat: add remove-duplicate-letters

Change-Id: Ia235c9510710931287527ccd0ee3b4bec3ea7ec5

README.md

@@ -218,6 +218,7 @@ LeetCode is a very good website to sharpen your programming/problem-solving skil
 |300|[Longest Increasing Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/)|[Java](./algorithms/longest-increasing-subsequence/)|![Medium](https://img.shields.io/badge/-Medium-orange)|
 |303|[Range Sum Query - Immutable](https://leetcode.com/problems/range-sum-query-immutable/)|[Java](./algorithms/range-sum-query-immutable/)|![Easy](https://img.shields.io/badge/-Easy-green)|
 |304|[Range Sum Query 2D - Immutable](https://leetcode.com/problems/range-sum-query-2d-immutable/)|[Java](./algorithms/range-sum-query-2d-immutable/)|![Medium](https://img.shields.io/badge/-Medium-orange)|
+|316|[Remove Duplicate Letters](https://leetcode.com/problems/remove-duplicate-letters/)|[Python](./algorithms/remove-duplicate-letters/)|![Medium](https://img.shields.io/badge/-Medium-orange)|
 |317|[Shortest Distance from All Buildings](https://leetcode.com/problems/shortest-distance-from-all-buildings/)|[Python](./algorithms/shortest-distance-from-all-buildings/)|![Hard](https://img.shields.io/badge/-Hard-red)|
 |328|[Odd Even Linked List](https://leetcode.com/problems/odd-even-linked-list/)|[Java](./algorithms/odd-even-linked-list/)|![Medium](https://img.shields.io/badge/-Medium-orange)|
 |330|[Patching Array](https://leetcode.com/problems/patching-array/)|[Java](./algorithms/patching-array/)|![Hard](https://img.shields.io/badge/-Hard-red)|
@@ -332,6 +333,7 @@ LeetCode is a very good website to sharpen your programming/problem-solving skil
 |1044|[Longest Duplicate Substring](https://leetcode.com/problems/longest-duplicate-substring/)|[Python](./algorithms/longest-duplicate-substring/)|![Hard](https://img.shields.io/badge/-Hard-red)|
 |1049|[Last Stone Weight II](https://leetcode.com/problems/last-stone-weight-ii/)|[Python](./algorithms/last-stone-weight-ii/)|![Medium](https://img.shields.io/badge/-Medium-orange)|
 |1071|[Greatest Common Divisor of Strings](https://leetcode.com/problems/greatest-common-divisor-of-strings/)|[Python](./algorithms/greatest-common-divisor-of-strings/)|![Easy](https://img.shields.io/badge/-Easy-green)|
+|1081|[Smallest Subsequence of Distinct Characters](https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/)|[Python](./algorithms/smallest-subsequence-of-distinct-characters/)|![Medium](https://img.shields.io/badge/-Medium-orange)|
 |1143|[Longest Common Subsequence](https://leetcode.com/problems/longest-common-subsequence/)|[Python](./algorithms/longest-common-subsequence/)|![Medium](https://img.shields.io/badge/-Medium-orange)|
 |1232|[Check If It Is a Straight Line](https://leetcode.com/problems/check-if-it-is-a-straight-line/)|[Python](./algorithms/check-if-it-is-a-straight-line/)|![Easy](https://img.shields.io/badge/-Easy-green)|
 |1277|[Count Square Submatrices with All Ones](https://leetcode.com/problems/count-square-submatrices-with-all-ones/)|[Python](./algorithms/count-square-submatrices-with-all-ones/)|![Medium](https://img.shields.io/badge/-Medium-orange)|

algorithms/remove-duplicate-letters/Solution.py

@@ -0,0 +1,39 @@
+"""
+Given a string s, remove duplicate letters so that every letter appears once and only once. You must make sure your result is the smallest in lexicographical order among all possible results.
+
+Note: This question is the same as 1081: https://leetcode.com/problems/smallest-subsequence-of-distinct-characters/
+
+ 
+
+Example 1:
+
+Input: s = "bcabc"
+Output: "abc"
+Example 2:
+
+Input: s = "cbacdcbc"
+Output: "acdb"
+ 
+
+Constraints:
+
+1 <= s.length <= 104
+s consists of lowercase English letters.
+
+"""
+
+
+class Solution:
+    def removeDuplicateLetters(self, s: str) -> str:
+        last_occ = {c: i for i, c in enumerate(s)}
+        stack = ["!"]
+        visited = set()
+
+        for i, symbol in enumerate(s):
+            if symbol in visited:
+                continue
+            while (symbol < stack[-1] and last_occ[stack[-1]] > i):
+                visited.remove(stack.pop())
+            stack.append(symbol)
+            visited.add(symbol)  
+        return "".join(stack)[1:]

algorithms/smallest-subsequence-of-distinct-characters/Solution.py

@@ -0,0 +1,38 @@
+"""
+Return the lexicographically smallest subsequence of s that contains all the distinct characters of s exactly once.
+
+Note: This question is the same as 316: https://leetcode.com/problems/remove-duplicate-letters/
+
+ 
+
+Example 1:
+
+Input: s = "bcabc"
+Output: "abc"
+Example 2:
+
+Input: s = "cbacdcbc"
+Output: "acdb"
+ 
+
+Constraints:
+
+1 <= s.length <= 1000
+s consists of lowercase English letters.
+
+"""
+
+class Solution:
+    def smallestSubsequence(self, s: str) -> str:
+        last_occ = {c: i for i, c in enumerate(s)}
+        stack = ["!"]
+        visited = set()
+
+        for i, symbol in enumerate(s):
+            if symbol in visited:
+                continue
+            while (symbol < stack[-1] and last_occ[stack[-1]] > i):
+                visited.remove(stack.pop())
+            stack.append(symbol)
+            visited.add(symbol)  
+        return "".join(stack)[1:]