34ms, 41%, 92%.

Author: Jeromestein

1209.remove-all-adjacent-duplicates-in-string-ii.java

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+/*
+ * @lc app=leetcode id=1209 lang=java
+ *
+ * [1209] Remove All Adjacent Duplicates in String II
+ */
+
+// @lc code=start
+
+class Solution {
+    public String removeDuplicates(String s, int k) {
+        StringBuilder sb = new StringBuilder(s);
+        Stack<Integer> counts = new Stack<>();
+        // walk through the string
+        for (int i = 0; i < sb.length(); ++i) {
+            if (i == 0 || sb.charAt(i) != sb.charAt(i - 1)) {
+                counts.push(1);
+            } else {
+                // If the current character is the same as the one before,
+                // increment the count on the top of the stack.
+                int incremented = counts.pop() + 1;
+                // If the count on the top of the stack equals k,
+                // erase last k characters and pop from the stack.
+                if (incremented == k) {
+                    sb.delete(i - k + 1, i + 1);
+                    i = i - k;
+                } else {
+                    counts.push(incremented);
+                }
+            }
+        }
+        return sb.toString();
+    }
+}
+// @lc code=end