| 3 | 3 | // convenience to get you started writing code faster. |
| 4 | 4 | // |
| 5 | 5 | |
| 6 | | export const encode = () => { |
| 7 | | throw new Error('Remove this line and implement the function'); |
| 6 | export const encode = (message, rails) => { |
| 7 | // Edge Case: Handle null or undefined message |
| 8 | if (message === null || message === undefined) { |
| 9 | return ''; |
| 10 | } |
| 11 | |
| 12 | // Edge Case: Handle zero or negative rails |
| 13 | if (rails <= 0) { |
| 14 | return ''; |
| 15 | } |
| 16 | |
| 17 | // Edge Case: Handle single rail |
| 18 | if (rails === 1) { |
| 19 | return message; |
| 20 | } |
| 21 | |
| 22 | // Edge Case: Handle empty message |
| 23 | if (message.length === 0) { |
| 24 | return ''; |
| 25 | } |
| 26 | |
| 27 | // Create an array for each rail |
| 28 | const fence = Array(rails).fill().map(() => []); |
| 29 | |
| 30 | let currentRail = 0; |
| 31 | let direction = 1; |
| 32 | |
| 33 | // Distribute characters across rails in a zigzag pattern |
| 34 | for (let i = 0; i < message.length; i++) { |
| 35 | fence[currentRail].push(message[i]); |
| 36 | |
| 37 | // Change direction when reaching top or bottom rail |
| 38 | if (currentRail === 0) { |
| 39 | direction = 1; |
| 40 | } else if (currentRail === rails - 1) { |
| 41 | direction = -1; |
| 42 | } |
| 43 | |
| 44 | currentRail += direction; |
| 45 | } |
| 46 | |
| 47 | // Concatenate all rails to form the encoded message |
| 48 | return fence.map(rail => rail.join('')).join(''); |
| 8 | 49 | }; |
| 9 | 50 | |
| 10 | | export const decode = () => { |
| 11 | | throw new Error('Remove this line and implement the function'); |
| 51 | export const decode = (encodedMessage, rails) => { |
| 52 | // Edge Case: Handle null or undefined encoded message |
| 53 | if (encodedMessage === null || encodedMessage === undefined) { |
| 54 | return ''; |
| 55 | } |
| 56 | |
| 57 | // Edge Case: Handle zero or negative rails |
| 58 | if (rails <= 0) { |
| 59 | return ''; |
| 60 | } |
| 61 | |
| 62 | // Edge Case: Handle single rail |
| 63 | if (rails === 1) { |
| 64 | return encodedMessage; |
| 65 | } |
| 66 | |
| 67 | // Edge Case: Handle empty encoded message |
| 68 | if (encodedMessage.length === 0) { |
| 69 | return ''; |
| 70 | } |
| 71 | |
| 72 | // Create a fence to map the zigzag pattern |
| 73 | const fence = Array(rails).fill().map(() => Array(encodedMessage.length).fill(null)); |
| 74 | |
| 75 | let currentRail = 0; |
| 76 | let direction = 1; |
| 77 | |
| 78 | // Mark the positions in the zigzag pattern |
| 79 | for (let i = 0; i < encodedMessage.length; i++) { |
| 80 | fence[currentRail][i] = true; |
| 81 | |
| 82 | if (currentRail === 0) { |
| 83 | direction = 1; |
| 84 | } else if (currentRail === rails - 1) { |
| 85 | direction = -1; |
| 86 | } |
| 87 | |
| 88 | currentRail += direction; |
| 89 | } |
| 90 | |
| 91 | // Fill the fence with characters from the encoded message |
| 92 | let charIndex = 0; |
| 93 | const result = Array(rails).fill().map(() => []); |
| 94 | |
| 95 | for (let r = 0; r < rails; r++) { |
| 96 | for (let c = 0; c < encodedMessage.length; c++) { |
| 97 | if (fence[r][c] === true) { |
| 98 | result[r][c] = encodedMessage[charIndex]; |
| 99 | charIndex++; |
| 100 | } |
| 101 | } |
| 102 | } |
| 103 | |
| 104 | // Read the message following the zigzag pattern |
| 105 | let decoded = ''; |
| 106 | currentRail = 0; |
| 107 | direction = 1; |
| 108 | |
| 109 | for (let i = 0; i < encodedMessage.length; i++) { |
| 110 | decoded += result[currentRail][i]; |
| 111 | |
| 112 | if (currentRail === 0) { |
| 113 | direction = 1; |
| 114 | } else if (currentRail === rails - 1) { |
| 115 | direction = -1; |
| 116 | } |
| 117 | |
| 118 | currentRail += direction; |
| 119 | } |
| 120 | |
| 121 | return decoded; |
| 12 | 122 | }; |
| 123 | |
| 124 | // Handled Edge Cases: null/undefined message, zero/negative rails, single rail, empty message |