Created
August 30, 2019 14:21
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| function railFenceCipher(operation, string, height = 3) { | |
| function encrypt(string, height, fence) { | |
| let currentRail = 0; | |
| let moveUp = true; | |
| let moveDown = false; | |
| for (let i = 0; i < fence[0].length; i += 1) { | |
| fence[currentRail].splice(i, 1, string[i]); | |
| if ((moveUp && currentRail + 1 > height - 1) || | |
| (moveDown && currentRail - 1 < 0)) { | |
| if (moveUp) currentRail -= 1; | |
| if (moveDown) currentRail += 1; | |
| moveUp = !moveUp; | |
| moveDown = !moveDown; | |
| } else if (moveUp) { | |
| currentRail += 1; | |
| } else if (moveDown) { | |
| currentRail -= 1; | |
| } | |
| } | |
| return fence.reduce((str, rail) => str += rail.filter(char => /\w/.test(char)).join(''), ''); | |
| } | |
| function decrypt(string, fence) { | |
| string = string.split(''); | |
| fence = fence.map(rail => rail.map(char => char === 'placeholder' ? string.shift() : char)); | |
| return fence.reduce((fence, rail) => fence += rail.join(' ') + '\n', ''); | |
| } | |
| function addPlaceholders(fence, numberOfRails) { | |
| let cycle = numberOfRails * 2 - 2; | |
| fence.forEach((rail, index) => { | |
| const processRail = (rail, railIndex) => { | |
| while (railIndex < rail.length ) { | |
| rail.splice(railIndex, 1, 'placeholder'); | |
| railIndex += cycle; | |
| } | |
| } | |
| let railIndex = index; | |
| let railNumber = index + 1; | |
| processRail(rail, railIndex); | |
| if (railNumber > 1 && railNumber < fence.length) { | |
| railIndex = cycle - railNumber + 1; | |
| processRail(rail, railIndex); | |
| } | |
| }); | |
| return fence; | |
| } | |
| if (operation === 'encrypt' && height === 1) { | |
| return 'Height must be 2 or more.'; | |
| } | |
| string = string.replace(/\W/g, ''); | |
| fence = [...Array(height)].map((_, i) => i) | |
| .map(rail => [...Array(string.length)].map((_, i) => i)) | |
| .map(rail => rail.map(element => '.')); | |
| if (operation === 'encrypt') { | |
| return encrypt(string, height, fence); | |
| } else if (operation === 'decrypt') { | |
| return decrypt(string, addPlaceholders(fence, height)); | |
| } | |
| } | |
| cipherText = 'WECRLTEERDSOEEFEAOCAIVDEN'; | |
| console.log(railFenceCipher('decrypt', cipherText, 3)); | |
| cipherText = '[IA_EZS]_ELYLK_UZERLIPL'; | |
| console.log(railFenceCipher('decrypt', cipherText, 3)); | |
| cipherText = 'INLLUCOOAHOVLSHEC'; | |
| console.log(railFenceCipher('decrypt', cipherText, 5)); | |
| message = 'WE ARE DISCOVERED FLEE AT ONCE'; | |
| console.log(railFenceCipher('encrypt', message, 3)); | |
| message = 'I LOVE LAUNCH SCHOOL!'; | |
| console.log(railFenceCipher('encrypt', message, 5)); |
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