Remove All Adjacent Duplicates In String

Problem Statement
You are given a string s consisting of lowercase English letters. A duplicate removal consists of choosing two adjacent and equal letters and removing them. We repeatedly make duplicate removals on s until we can no longer do so. Return the final string after all such duplicate removals have been made.[1][9]

Input/Output Examples

• Input: s = "abccba"
  Output: ""
  Explanation: Remove "cc" → "abba"; remove "bb" → "aa"; remove "aa" → empty string.[1]

• Input: s = "foobar"
  Output: "fbar"
  Explanation: Remove "oo" → "fbar".[1]

• Input: s = "fooobar"
  Output: "fobar"
  Explanation: Remove "oo" → "fobar".[1]

• Input: s = "abcd"
  Output: "abcd"
  Explanation: No adjacent duplicates, so no changes.[1]

Additional common example from sources:

• Input: s = "azxxzy"
  Output: "ca"
  Explanation: Remove "xx" and "zz" step-by-step via stack simulation.[2]

Constraints

• 1 <= s.length <= 10^5
• s consists of lowercase English letters.[1]