Added Leetcode Solution 1209

dsa-solutions/lc-solutions/1200-1299/1209-remove-all-adjacent-duplicates-in-string-II.md

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+---
+id: remove-all-adjacent-duplicates-in-string-II
+title: Remove All Adjacent Duplicates in String II
+sidebar_label: 1209. Remove All Adjacent Duplicates in String II
+tags:
+  - String
+  - Stack
+description: "Solution to Leetcode 1209. Remove All Adjacent Duplicates in String II"
+---
+
+## Problem Description
+
+You are given a string s and an integer k, a k duplicate removal consists of choosing k adjacent and equal letters from s and removing them, causing the left and the right side of the deleted substring to concatenate together.
+
+We repeatedly make k duplicate removals on s until we no longer can.
+
+Return the final string after all such duplicate removals have been made. It is guaranteed that the answer is unique.
+
+### Examples
+
+**Example 1:**
+
+```
+Input: s = "abcd", k = 2
+Output: "abcd"
+Explanation: There's nothing to delete.
+```
+
+**Example 2:**
+
+```
+Input: s = "deeedbbcccbdaa", k = 3
+Output: "aa"
+Explanation:
+First delete "eee" and "ccc", get "ddbbbdaa"
+Then delete "bbb", get "dddaa"
+Finally delete "ddd", get "aa"
+```
+
+### Constraints
+
+- `1 <= s.length <= 10^5`
+- `2 <= k <= 10^4`
+
+### Approach
+
+1. Save the character c and its count to the stack.
+2. If the next character c is same as the last one, increment the count.
+3. Otherwise push a pair (c, 1) into the stack.
+4. I used a dummy element ('#', 0) to avoid empty stack.
+
+### Complexity
+
+Time complexity: $O(n)$
+Space complexity: $O(n)$
+
+### Solution
+
+#### Code in Different Languages
+
+#### C++
+
+```cpp
+    string removeDuplicates(string s, int k) {
+       vector<pair<int, char>> stack = {{0, '#'}};
+       for (char c: s) {
+           if (stack.back().second != c) {
+               stack.push_back({1, c});
+           } else if (++stack.back().first == k)
+               stack.pop_back();
+       }
+       string res;
+       for (auto & p : stack) {
+           res.append(p.first, p.second);
+       }
+       return res;
+    }
+```
+
+#### JAVA
+
+```java
+    public String removeDuplicates(String s, int k) {
+        int[] count = new int[s.length()];
+        StringBuilder sb = new StringBuilder();
+        for(char c : s.toCharArray()) {
+            sb.append(c);
+            int last = sb.length()-1;
+            count[last] = 1 + (last > 0 && sb.charAt(last) == sb.charAt(last-1) ? count[last-1] : 0);
+            if(count[last] >= k) sb.delete(sb.length()-k, sb.length());
+        }
+    return sb.toString();
+    }
+```
+
+#### PYTHON
+
+```python
+    def removeDuplicates(self, s, k):
+        stack = [['#', 0]]
+        for c in s:
+            if stack[-1][0] == c:
+                stack[-1][1] += 1
+                if stack[-1][1] == k:
+                    stack.pop()
+            else:
+                stack.append([c, 1])
+        return ''.join(c * k for c, k in stack)
+```
+
+### Complexity Analysis
+
+- Time Complexity: $O(n)$
+
+- Space Complexity: $O(n)$
+
+### References
+
+- **LeetCode Problem**: Remove All Adjacent Duplicates in String II