Simple Vertical Cipher Algorithm

Given a string s and an integer n, rearrange s into n rows so that s can be read vertically (top-down, left to right).

Constraints
Length of s ≤ 10000
n ≤ 1000
Example 1
Input
s = “abcdefghi”
n = 5
Output

1	["af", "bg", "ch", "di", "e"]

["af", "bg", "ch", "di", "e"]

Explanation
This reads vertically as:

1 2 3 4 5

["af",  "bg",  "ch",  "di",  "e"]

["af",
 "bg",
 "ch",
 "di",
 "e"]

Simple Vertical Cipher in C++

We know the transformed result has n rows, thus we can allocate vector of N size. Then going through each character of the string, we append it to the corresponding row – which we can easily increment the row and remember to rewind to the first row by modulus operator ie. %.

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vector<string> verticalCipher(string s, int n) {
    vector<string> ans(n, "");
    int r = 0;
    for (auto &c: s) {
        ans[r].push_back(c);
        r = (r + 1) % n;
    }
    return ans;
}

vector<string> verticalCipher(string s, int n) {
    vector<string> ans(n, "");
    int r = 0;
    for (auto &c: s) {
        ans[r].push_back(c);
        r = (r + 1) % n;
    }
    return ans;
}

Time complexity for this simple string cipher is O(N) where N is the number of the characters in the original string.

String Cipher Algorithms

• Simple Vigenère Cipher in C++
• A Simple Atbash Cipher
• Simple Vertical Cipher Algorithm
• Caesar Cipher Algorithm in C++

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