I am trying to develop a function named decode(message_file). This function should read an encoded message from a .txt file and return its decoded version as a string. The function must be able to process an input file with the following format:
3 love
6 computers
2 dogs
4 cats
1 I
5 you
In this file, each line contains a number followed by a word. The task is to decode a hidden message based on the arrangement of these numbers into a "pyramid" structure. The pyramid increases by one number per line, like so:
1
2 3
4 5 6
The key to decoding the message is to use the words corresponding to the numbers at the end of each pyramid line (in this example, 1, 3, and 6). You should ignore all the other words.
I'm having difficulty obtaining the desired result.
Here's the code I've tried:
function decode(input) {
const lines = input.trim().split('\n');
let decodedWords = [];
let currentIndex = 0;
for (const line of lines) {
const words = line.trim().split(' ');
const currentWord = words[currentIndex];
decodedWords.push(currentWord);
currentIndex++;
}
return decodedWords.join(' ');
}
const input = `3 love
6 computers
2 dogs
4 cats
1 I
5 you`;
const message = decode(input);
console.log(message);
My current code is producing the output of 3 computers when I need it to produce I love computers
After we get this working, I need it to decode the contents of this list:
195 land
235 sun
111 too
60 huge
5 dont
229 such
15 noun
176 student
136 brown
248 complete
36 play
65 cook
221 yard
84 clock
231 would
183 plain
187 excite
199 fire
298 wish
39 cool
91 child
148 past
118 colony
292 oil
287 dog
184 back
280 money
138 kind
249 open
102 finger
14 touch
252 are
99 dad
227 am
125 modern
140 meant
55 ocean
270 pitch
132 suit
154 town
22 east
126 over
3 group
179 good
19 kind
71 down
134 band
1 especially
117 organ
49 of
200 fire
17 out
212 area
69 touch
166 happen
238 sat
274 electric
104 wrote
262 buy
172 lot
152 stop
43 corn
137 where
239 check
41 live
9 best
77 hold
300 cause
246 grand
59 present
21 indicate
62 counter
288 we
265 like
109 visit
57 state
10 morning
198 true
224 are
218 ball
207 history
188 seat
165 rain
119 less
233 glass
214 tone
220 song
38 fair
4 element
243 speed
223 produce
80 quotient
112 sand
50 begin
32 moment
258 offer
276 probable
163 all
97 necessary
295 post
106 cent
240 happen
267 speech
259 object
196 silver
192 third
156 crease
26 wait
285 triangle
257 idea
100 clothe
289 young
237 discuss
282 field
95 company
64 capital
13 compare
268 chart
129 possible
293 written
46 remember
236 mile
234 cold
34 lady
93 felt
170 against
56 skin
250 prepare
153 he
186 card
201 organ
205 object
115 our
70 major
27 discuss
45 system
245 hole
272 above
76 they
58 produce
244 straight
160 level
266 though
54 modern
294 dry
37 bought
180 milk
279 make
185 show
178 middle
52 center
35 blood
261 speak
122 prove
281 select
173 power
225 come
121 brown
63 experiment
18 strong
89 hurry
159 touch
105 reach
269 case
47 beat
73 over
251 dry
94 hill
48 company
273 opposite
290 work
226 field
263 felt
213 prepare
6 now
260 his
168 stay
189 toward
133 observe
197 time
81 stop
66 possible
169 card
31 prepare
11 current
28 compare
151 neighbor
222 thus
33 include
40 copy
85 bit
283 stead
164 does
78 general
175 solve
182 glad
158 duck
74 offer
44 happen
216 ball
123 bread
161 like
171 machine
145 come
299 any
24 band
147 it
255 section
96 close
30 heavy
194 produce
232 got
254 possible
2 insect
215 way
150 before
217 men
209 bird
8 ease
98 trade
83 winter
131 am
42 repeat
113 first
120 to
253 each
162 guide
67 column
103 single
20 remember
228 wild
146 major
75 coast
114 class
135 done
157 jump
242 sister
149 feel
88 check
7 fire
167 nine
29 indicate
92 parent
277 whole
128 her
124 the
203 temperature
202 design
16 big
53 skill
296 friend
286 hit
116 wait
141 instant
291 blow
210 about
143 chick
275 answer
110 man
191 material
208 current
177 think
144 print
181 nor
51 better
247 example
155 people
79 drink
284 gun
174 together
90 cost
142 require
68 or
206 people
72 planet
25 ease
264 ready
82 enough
87 sugar
127 deal
130 with
101 us
204 share
139 office
230 protect
12 low
241 thus
193 farm
278 oxygen
190 fire
86 force
211 select
297 paragraph
107 always
108 poem
271 chick
256 planet
23 fact
61 moment
219 term
The general idea is to first parse the file then sort the obtained entries by the number and then calculate the positions of the last element in a line in a pyramid until we reach the end of the array.
To do that you have to image that you flatten the pyramid to an array i. e.
1
2 3
4 5 6
becomes
+---+---+---+---+---+---+
Value | 1 | 2 | 3 | 4 | 5 | 6 |
+---+---+---+---+---+---+
Index 0 1 2 3 4 5
With that in mind the most challenging thing is coming up with a working formula that can give you the position of the last element in a row within the pyramid i. e. an index within the array based on the row you are at. We can derive this if we have a look at the first couple of rows:
index := index of the element at the end of the row in a pyramid within the array
| height | pyramid | index | diff to height + 1 | Previous index | Calculation |
|---|---|---|---|---|---|
| 0 | 1 | 0 | 2 | - | 0 |
| 1 | 2 3 | 2 | 3 | 0 | 0 + 1 + 1 = 2 |
| 2 | 4 5 6 | 5 | 4 | 2 | 2 + 2 + 2 = 5 |
| 3 | 7 8 9 10 | 9 | 5 | 5 | 5 + 3 + 1 = 9 |
| 4 | 11 12 13 14 15 | 14 | 6 | 9 | 9 + 4 + 1 = 14 |
Looking at that we can conclude that we can use the following formula:
new index = previous index + height + 1
Obviously the first index is always 0, so we can use that as a start value.
Using that formula we now have to just iterate through the array and pick out the words. Last but not least we need to concatenate them.
/**
* A token
* @typedef {Object} Token
* @property {number} index - Number in a line
* @property {string} word - Word next to the number in a line
*/
/**
* Parses string of words and indices
* @param {string} input string of words and indices
* @returns {Array<Token>} list of tokens
*/
const parse = (input) =>
input
.trim()
.split("\n")
.map((x) => {
const [index, word] = x.split(" ");
return { index: parseInt(index), word };
});
// Formula: new index = previous index + height + 1
// height | pyramid | index | diff to height + 1 | Previous index | Calculation |
//--------|------------------|-------|----------------------|----------------|----------------|
// 0 | 1 | 0 | 2 | - | 0 |
// 1 | 2 3 | 2 | 3 | 0 | 0 + 1 + 1 = 2 |
// 2 | 4 5 6 | 5 | 4 | 2 | 2 + 2 + 2 = 5 |
// 3 | 7 8 9 10 | 9 | 5 | 5 | 5 + 3 + 1 = 9 |
// 4 | 11 12 13 14 15 | 14 | 6 | 9 | 9 + 4 + 1 = 14 |
// ...
/**
* Decode tokens to sentence.
* @param {Array<Token>} tokens
* @returns {string} decoded sentence
*/
const decode = (tokens) => {
// sort tokens
// This takes O(n log n) but with counting sort you can bring this down to O(n + k) with k being the range of your input number 1-300 here
const sortedTokens = tokens.toSorted((a, b) => a.index - b.index);
// actual decode
let height = 0;
const wordsOfSentence = [];
for (let index = 0; index < sortedTokens.length; index = index + height + 1) {
const word = sortedTokens[index].word;
wordsOfSentence.push(word);
height++;
}
return wordsOfSentence.join(" ");
};
const longSentence = `195 land
235 sun
111 too
60 huge
5 dont
229 such
15 noun
176 student
136 brown
248 complete
36 play
65 cook
221 yard
84 clock
231 would
183 plain
187 excite
199 fire
298 wish
39 cool
91 child
148 past
118 colony
292 oil
287 dog
184 back
280 money
138 kind
249 open
102 finger
14 touch
252 are
99 dad
227 am
125 modern
140 meant
55 ocean
270 pitch
132 suit
154 town
22 east
126 over
3 group
179 good
19 kind
71 down
134 band
1 especially
117 organ
49 of
200 fire
17 out
212 area
69 touch
166 happen
238 sat
274 electric
104 wrote
262 buy
172 lot
152 stop
43 corn
137 where
239 check
41 live
9 best
77 hold
300 cause
246 grand
59 present
21 indicate
62 counter
288 we
265 like
109 visit
57 state
10 morning
198 true
224 are
218 ball
207 history
188 seat
165 rain
119 less
233 glass
214 tone
220 song
38 fair
4 element
243 speed
223 produce
80 quotient
112 sand
50 begin
32 moment
258 offer
276 probable
163 all
97 necessary
295 post
106 cent
240 happen
267 speech
259 object
196 silver
192 third
156 crease
26 wait
285 triangle
257 idea
100 clothe
289 young
237 discuss
282 field
95 company
64 capital
13 compare
268 chart
129 possible
293 written
46 remember
236 mile
234 cold
34 lady
93 felt
170 against
56 skin
250 prepare
153 he
186 card
201 organ
205 object
115 our
70 major
27 discuss
45 system
245 hole
272 above
76 they
58 produce
244 straight
160 level
266 though
54 modern
294 dry
37 bought
180 milk
279 make
185 show
178 middle
52 center
35 blood
261 speak
122 prove
281 select
173 power
225 come
121 brown
63 experiment
18 strong
89 hurry
159 touch
105 reach
269 case
47 beat
73 over
251 dry
94 hill
48 company
273 opposite
290 work
226 field
263 felt
213 prepare
6 now
260 his
168 stay
189 toward
133 observe
197 time
81 stop
66 possible
169 card
31 prepare
11 current
28 compare
151 neighbor
222 thus
33 include
40 copy
85 bit
283 stead
164 does
78 general
175 solve
182 glad
158 duck
74 offer
44 happen
216 ball
123 bread
161 like
171 machine
145 come
299 any
24 band
147 it
255 section
96 close
30 heavy
194 produce
232 got
254 possible
2 insect
215 way
150 before
217 men
209 bird
8 ease
98 trade
83 winter
131 am
42 repeat
113 first
120 to
253 each
162 guide
67 column
103 single
20 remember
228 wild
146 major
75 coast
114 class
135 done
157 jump
242 sister
149 feel
88 check
7 fire
167 nine
29 indicate
92 parent
277 whole
128 her
124 the
203 temperature
202 design
16 big
53 skill
296 friend
286 hit
116 wait
141 instant
291 blow
210 about
143 chick
275 answer
110 man
191 material
208 current
177 think
144 print
181 nor
51 better
247 example
155 people
79 drink
284 gun
174 together
90 cost
142 require
68 or
206 people
72 planet
25 ease
264 ready
82 enough
87 sugar
127 deal
130 with
101 us
204 share
139 office
230 protect
12 low
241 thus
193 farm
278 oxygen
190 fire
86 force
211 select
297 paragraph
107 always
108 poem
271 chick
256 planet
23 fact
61 moment
219 term`;
const shortSentence = `3 love
6 computers
2 dogs
4 cats
1 I
5 you`;
/**
* Process input and log result
* @param {string} input input
*/
const process = (input) => {
const tokens = parse(input);
return decode(tokens);
};
console.log(`Short sentence decoded: ${process(shortSentence)}`);
console.log(`Long sentence decoded: ${process(longSentence)}`);/* Stackoverflow: show only console */
.as-console-wrapper {
max-height: 100% !important;
top: 0;
}I noticed that the long sentence decoded does not make much sense, but the algorithm should be correct (I've crossed check the first couple words manually and they are correct but don't make much sense as a sentence either). Might be that I made an error copying the words although I've checked at least the first couple words or your input and not seen any errors there or your input is not properly encoded or there is another element to the algorithm which I might have missed or you've missed in the specification.
The runtime depends on how fast you can sort with this approach. As currently implemented this runs in O(n log n) because general sort algorithms based on comparisons cannot be faster than that. But you could use counting sort here which would give you linear runtime O(n+k), where k is the range of the non-negative key values for sorting.