当位置超出范围时如何从数组中选择一个值？

Question

我正在尝试使用特定方法加密一些明文。给定一个密钥 [4,5,6,7] 和明文“这是一些明文” 第一个字母是 T 密钥中的第一个数字是 4 因此 T 通过向前移动变成 X 4 (T, U, V, W, X)字母是 H 键是 5 因此 H 变成 M {H, I, J, K, L, M}

当到达密钥的末尾时，只需从头开始并继续加密直到完成。我有一个 Python 的基本大纲：

#key = [4,5,12,6,7,11,8,9,1,2,3,10]
key = [4,5,6,7]
letters = ["A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"]
plaintext = "IfyouarereadingthisthenthisplanetmayhavehopeafterallYouhavethepowerand"
plaintext = plaintext.upper()
keySpot = 0
count = 0;
keyCount = 0
letterLocation = 0
tempLetter = ""
i = 0

while(count < len(plaintext)):
    tempLetter = plaintext[count]
    for i in range(0, len(letters)):
        if(tempLetter == letters[i]):
            letterLocation = i
        i = i + 1

    if(keyCount > 4):
    keyCount = 0

letterLocation = letterLocation + key[keyCount]
keyCount = keyCount + 1

if(letterLocation > 27):
    #need some logic here so it wont go out of bounds

print letters[letterLocation]
count = count + 1

我的主要问题是，如果 letterLocation 在前进并超过 Z 时太大，该怎么办。当它到达 Z 时，我需要它从 A 处重新开始并继续前进直到完成。例如，如果明文字母为 Y，密钥为 5，Y 将变为 D {Y, Z, A, B, C, D}

我该怎么做？它可以是 Java、C、C++、JavaScript 或 Python，只要是最简单的。如果你能想出更好的方法，我会采纳建议的。

Answer 1

嗯，这很简单，只需使用模数：

letterLocation = (letterLocation + key[keyCount]) % 26