1047. Remove All Adjacent Duplicates In String

  • Hardness: \(\color{green}\textsf{Easy}\)
  • Ralated Topics: String、Stack

一、題目

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 repeatly make duplicate removals on s until we no longer can.

Return the final string after all such duplicate removals have been made. It can be proven that the answer is unique.

Example 1:

  • Input: s = “abbaca”
  • Output: “ca”
  • Explanation: For example, in “abbaca” we could remove “bb” since the letters are adjacent and equal, and this is the only possible move. The result of this move is that the string is “aaca”, of which only “aa” is possible, so the final string is “ca”.

Example 2:

  • Input: s = “azxxzy”
  • Output: “ay”

Constraints:

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

二、分析

  • 因為本題是連續移除，可運用 Stack 的概念，只要出現跟堆頂字元相同時，就 pop 掉堆頂。

三、解題

1. Stack

  • Time complexity: \(O(n)\)
  • Space complexity: \(O(n)\)
string removeDuplicates(string s) {
    string res = "";
    for (char c : s) {
        if (res.empty()) {
            res.push_back(c);
        } else {
            if (res.back() == c) {
                res.pop_back(); 
            } else {
                res.push_back(c);
            }
        }
    }
    return res;
}

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