加密后无法得到正确的字母

Question

I am working on this problem at CodeWars: Vowels Back Usually half of my tests fail, but from what I see every fail test is because of letter 'a' since I get '\backslash' instead of 'v'. Of course, I see from my calculations why I get '\backslash', I tried to fix it with something like Math.abs(), but then I was getting 'f', not 'v'. Can someone help me fix this please? All other letter changes seem correct.

 function vowelBack(s){ let output = ''; let position; let newPosition; let newChar; for (let i = 0; i < s.length; i++) { position = s.charCodeAt(i); if (s[i] === 'c' || s[i] === 'o') { newPosition = ((position - 97 - 1) % 26) + 97; newChar = String.fromCharCode(newPosition); if (newChar === 'c' || newChar === 'o' || newChar === 'd' || newChar === 'e') { newChar = s[i]; } output += newChar; } else if (s[i] === 'd') { newPosition = ((position - 97 - 3) % 26) + 97; newChar = String.fromCharCode(newPosition); if (newChar === 'c' || newChar === 'o' || newChar === 'd' || newChar === 'e') { newChar = s[i]; } output += newChar; } else if (s[i] === 'e') { newPosition = ((position - 97 - 4) % 26) + 97; newChar = String.fromCharCode(newPosition); if (newChar === 'c' || newChar === 'o' || newChar === 'd' || newChar === 'e') { newChar = s[i]; } output += newChar; } else if (s[i] === 'a' || s[i] === 'i' || s[i] === 'u') { newPosition = ((position - 97 - 5) % 26) + 97; newChar = String.fromCharCode(newPosition); if (newChar === 'c' || newChar === 'o' || newChar === 'd' || newChar === 'e') { newChar = s[i]; } output += newChar; } else { newPosition = ((position - 97 + 9) % 26) + 97; newChar = String.fromCharCode(newPosition); if (newChar === 'c' || newChar === 'o' || newChar === 'd' || newChar === 'e') { newChar = s[i]; } output += newChar; } } return output; } console.log(vowelBack("testcase"));

Answer 1

In javascript, -b < (a % b) < b , as opposed to 0 <= (a % b) < b in mathmatical notation (so -1 % 5 == -1 , not 4 ). To ensure a positive solution, write (((a % b) + b) % b) .

In your situation, I would add a function:

function shiftLetter(position, shift) {
    return ((((position - 97 + shift) % 26) + 26) % 26) + 97;
}