C#LeetCode刷题之#844-比较含退格的字符串（Backspace String Compare）

问题

给定 S 和 T 两个字符串，当它们分别被输入到空白的文本编辑器后，判断二者是否相等，并返回结果。 # 代表退格字符。

输入：S = "ab#c", T = "ad#c"

输出：true

解释：S 和 T 都会变成 “ac”。

输入：S = "ab##", T = "c#d#"

输出：true

解释：S 和 T 都会变成 “”。

输入：S = "a##c", T = "#a#c"

输出：true

解释：S 和 T 都会变成 “c”。

输入：S = "a#c", T = "b"

输出：false

解释：S 会变成 “c”，但 T 仍然是 “b”。

提示：

• 1 <= S.length <= 200
• 1 <= T.length <= 200
• S 和 T 只含有小写字母以及字符 '#'。

---

Given two strings S and T, return if they are equal when both are typed into empty text editors. # means a backspace character.

Input: S = "ab#c", T = "ad#c"

Output: true

Explanation: Both S and T become "ac".

Input: S = "ab##", T = "c#d#"

Output: true

Explanation: Both S and T become "".

Input: S = "a##c", T = "#a#c"

Output: true

Explanation: Both S and T become "c".

Input: S = "a#c", T = "b"

Output: false

Explanation: S becomes "c" while T becomes "b".

Note:

• 1 <= S.length <= 200
• 1 <= T.length <= 200
• S and T only contain lowercase letters and '#' characters.

---

示例

public class Program {

    public static void Main(string[] args) {
        var S = "ab#c";
        var T = "ad#c";

        var res = BackspaceCompare(S, T);
        Console.WriteLine(res);

        S = "a#c";
        T = "b#cd";

        res = BackspaceCompare2(S, T);
        Console.WriteLine(res);

        Console.ReadKey();
    }

    private static bool BackspaceCompare(string S, string T) {
        var stackS = GetStack(S);
        var stackT = GetStack(T);
        if(stackS.Count != stackT.Count) return false;
        for(var i = 0; i < stackS.Count; i++) {
            if(stackS.ElementAt(i) != stackT.ElementAt(i))
                return false;
        }
        return true;
    }

    private static Stack GetStack(string S) {
        var stack = new Stack();
        foreach(var c in S) {
            if(c == '#') {
                if(stack.Count != 0) stack.Pop();
            } else {
                stack.Push(c);
            }
        }
        return stack;
    }

    private static bool BackspaceCompare2(string S, string T) {
        var sb1 = GetStringBuilder(S);
        var sb2 = GetStringBuilder(T);
        return sb1.ToString() == sb2.ToString();
    }

    private static StringBuilder GetStringBuilder(string S) {
        var sb = new StringBuilder();
        for(var i = 0; i < S.Length; ++i) {
            if(S[i] == '#') {
                if(sb.Length > 0) sb.Remove(sb.Length - 1, 1);
            } else sb.Append(S[i]);
        }
        return sb;
    }

}

以上给出2种算法实现，以下是这个案例的输出结果：

True
False

---

分析：

设 S 和 T 两个单词中最长的单词的字符数为 n，那么显而易见，以上2种算法的时间复杂度均为：  。