Possible words from Phone Digits | letter combination of a Phone number | Decoding Recursion
Possible words from Phone Digits | letter combination of a Phone number | Decoding Recursion
Here in this video, we have solved a problem letter combination of a phone number. Watch it till the end, to understand it completely. Also share it with your friends if you find these lectures helpful.
Problem link: https://practice.geeksforgeeks.org/pr…
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Content
0 -> Hi guys welcome to code in 10. I am Nishant Chahar
2.392 -> So in today's video we gonna talk about this question, the name is "possible words from a phone digit"
7.48 -> Now what is given in that
9.018 -> You will be given an array
10.725 -> In which you will be told that
12.151 -> Which digits are used here
14.702 -> Which digits are pressed here
16.029 -> We have to give output
17.187 -> Which words were possible
18.647 -> If you are 90's kid
20.907 -> If you are born in 2000,2001, 2002, 2003,2004,2005
24.052 -> So you must have played with this phone
25.936 -> Nokia's phone used to come
27.697 -> Reliance phones used to come
28.505 -> In those, there used to be nice games
29.515 -> Okay
30.229 -> There used to be a bounce game in Nokia's phones
32.02 -> So when we used to text in that
34.112 -> So we will have to press a keyword 2-3 times
36.469 -> Like if We want to write c
38.24 -> So we had to press 2 button 3 times
40.901 -> Similarly if we want to write z
43.153 -> We had to press 9 button four times
45.023 -> It used to be very difficult
46.13 -> So we just have to tell
47.992 -> How many possible words can be made
49.109 -> We will take a small example
50.573 -> We will solve for n= 2
52.89 -> After that we will write its code
55.77 -> Then we will explain you
56.69 -> So lets start the video without any delay
58.358 -> Lets consider
59.898 -> That we have n =2
62.714 -> The array that you are given
64.099 -> In that you are given 2,4
66.435 -> So lets paste that keyboard here
69.536 -> Okay
70.211 -> So if you see on this keyboard
72.357 -> This is abc
74.445 -> And on 4 it is ghi
76.581 -> So we have to tell that how many multiple words are possible in it
81.128 -> So if you see
82.597 -> If we will press 2
83.921 -> we have 3 options
85.029 -> A, B and C
87.146 -> Okay
88.019 -> First time we pressed 2, so any one button can be used from them
90.778 -> We again have 3 options
92.408 -> either we will use g or h or i
96.763 -> Similarly here g, h and i
99.524 -> Similarly g, h and i
103.635 -> It will be made separately for everyone
105.062 -> in one, it will be AG
106.267 -> in one it will be AH
109.582 -> And in one, it will be AI
112.432 -> Okay
113.236 -> Similarly same will happen for B
114.78 -> And for C also
115.6 -> So total we will
117.501 -> 3+3+3 that is 9
120.621 -> Okay
122.103 -> So you have to do nothing
123.309 -> The basic subsets and subsequences that we are doing till now
127.454 -> What we do is we tell recursion
128.921 -> That I have done my work on this position
132.467 -> Bring all the that can be possible from the further
136.468 -> And tell me how many answers can be there
138.685 -> Here also we will do the same thing
140.846 -> We will say that in a loop
142.331 -> Currently I am at 2
147.517 -> So I will say
149.088 -> That I have abc in 2
151.525 -> So first bring on a
153.975 -> Make a temporary
155.949 -> And tell him that I have added A in my current string
158.975 -> You go. If I will press 4
161.382 -> How many multiple answers can come. Bring me all of that
163.755 -> So it will bring AG
165.5 -> It will bring AH
167.367 -> and AI
168.692 -> Then we will say
169.542 -> A, your work has done
170.845 -> Now lets do B in place of A
172.719 -> And then we will say B to do the same work
174.954 -> And likewise do C
176.88 -> Then we will ask C to do the same work
178.581 -> In this way all of our strings will be generated
182.481 -> Okay
183.971 -> I hope you understood a little bit
185.308 -> What we guys do is lets take a big example
187.228 -> Try solving that
188.104 -> So what we said, we took n=3
190.211 -> We said
191.244 -> if we are given 2,3,4
193.584 -> Then tell what will be generated
195.452 -> 2 has ABC
196.957 -> 3 has DEF
200.77 -> And 4 has GHI
204.251 -> So now what we will do
205.77 -> We have 3 places
206.829 -> First we will say add all that are possible in 2
208.914 -> Once put A, once put B, once put C
211.526 -> Now tell A and bring second place fill
214.07 -> We have to see 3 at second place what is there on 3
216.459 -> On 3 we can put DEF
217.932 -> Once we will do AD, once AE, once AF
223.506 -> After happening of this, We will say the Ad happened
225.913 -> one 3rd place left
227.358 -> go on 3rd place
229.368 -> And do your further work
231.953 -> What it will do on 3rd place
233.436 -> It will see on 4th that GH has come
235.237 -> like lets take f
236.572 -> What it will say
237.728 -> this became AF
239.746 -> Put G in it
241.073 -> AF happened, now put H in it
243.007 -> AF happened, now put I in it
245.035 -> So doing like this many will be made
247.937 -> If you will try making
249.343 -> Just go on index i
251.424 -> try putting all the possible value there
254.749 -> And tell recursion that bring all after this
258.414 -> Okay
259.151 -> We have done the small calculations that we had to do
261.442 -> No we will apply recursive call
262.646 -> You bring your answer and give us
264.035 -> Our work is done
264.941 -> Now lets write code
266.447 -> We will solve it with code
268.353 -> It will be more clear to you
269.995 -> So what we do first
271.715 -> I have put all of my possible keys here for zero
274.231 -> There is no zero here
275.963 -> But because all of our indexes start from 0
279.41 -> So for simplicity, here it is 1,2,3,4,5,6,7
284.242 -> This is 8,9
285.344 -> No what we do lets make our vector
287.185 -> In which we have to give answer
288.378 -> We will make that same helper function
291.972 -> In it we will also say
295.054 -> That give me your array
296.709 -> Give me size of array
299.389 -> Okay
300.495 -> Let me make a temporary string
302.188 -> Other than that let me make index i
304.426 -> Now that same base case. If the value of i become equal to n
308.416 -> So say
309.791 -> push back in answer
311.421 -> my current temporary string
314.783 -> and return from here and your work has done
317.539 -> Now next we have to write this loop
319.846 -> What we have to say in the loop
321.423 -> That start j from 0
324.325 -> And this is in the keys
327.784 -> What we have to do
329.142 -> That until j's value to keys a of i is less than, keep doing j++
338.986 -> Okay lets understand once
340.321 -> That what is this a of i's value
342.506 -> a of i's value is what we are given here
344.112 -> So it is 2
345.881 -> So what will be the value at 2 of keys, it will be ABC
348.17 -> Only what you have to do, the size of ABC
351.443 -> j should always be smaller than ABC's size until we have to run the code
355.893 -> Okay understood
356.899 -> Now we have to do nothing
358.171 -> Call the helper function
359.455 -> Tell it that this is your array
361.962 -> This is n
363.406 -> Give us by adding in temporary string
366.333 -> What we have to do with keys
367.925 -> a of i's
369.655 -> a of i
371.296 -> After that what we have to do j
372.638 -> , will call i++
374.883 -> Now what is this
378.244 -> When we will code,I will show you then
380.295 -> This means a of i will be ABC
386.398 -> If we take j of ABC as 0
388.543 -> So the value will be a
389.95 -> We said that add a in temporary
392.844 -> Then call the recursion
394.388 -> What was index ?
396.902 -> It was 0
398.611 -> Do 0 as 1
399.878 -> And after that do sum
401.223 -> We have to do nothing. Our code is done
403.233 -> Now we will tell helper
405.158 -> Take a and go
408.094 -> Take n
409.236 -> Take temporary empty string
411.302 -> Take index 0
412.758 -> Return my answer
414.484 -> Work is done
415.458 -> Lets run it now
416.745 -> So it is right
421.877 -> Submit it
423.56 -> This is submitted
429.454 -> Okay now lets try to understand
431.319 -> So now what is happening
434.474 -> The value of a is 2,4
436.962 -> And the value of n is 2
439.247 -> No what we do
440.386 -> empty the temporary
442.141 -> And currently our index is i = 0
444.202 -> So what we said
445.828 -> That called the recursion
447.04 -> Here it became 2
448.541 -> This became our 2
450.11 -> Then we called the recursion
452.89 -> This is our array a, this is n, this temporary is currently empty
455.852 -> And the value of i is 0
456.887 -> We said if the value of i is equal to n, no
458.678 -> n is 2
459.996 -> So it will not go in the if
461.398 -> It will directly come to for loop
462.545 -> In for loop the value of j is 0
463.951 -> Okay
464.845 -> And now we will see
466.737 -> Keys a of i
467.799 -> Okay
468.638 -> What is keys a of i
469.943 -> A of i is
471.703 -> We got value of a of i as 2
474.331 -> Okay
475.556 -> So now we will say that the element that is on second position at keys
478.094 -> Bring that
478.963 -> We have 0,1,2 at second
481.628 -> At 2 we have ABC
482.655 -> We said what is the size of ABC. The size of ABC is 3
485.709 -> So what we will do until j is less than 3
488.025 -> Keep running it until then
489.441 -> And do j++
490.688 -> What we told helper
492.618 -> Keep a
494.022 -> Take n again
494.764 -> And temp was empty
495.857 -> And in empty keys of a of i
499.098 -> We saw here a of i is 2
500.336 -> So what will happen of keys 2
502.024 -> After this, next is j
504.6 -> j is 0
505.124 -> So ABC is a string itself
508.401 -> We know it is also 0,1,2
510.755 -> So we said its zeroth element
513.331 -> That is a
515.73 -> So add with temp
517.073 -> So here a will be added
518.576 -> And do recursion call here
520.424 -> Okay so now it will call recursion
522.03 -> Okay
523.404 -> Like we saw here
524.656 -> Now it will call the recursion
525.819 -> Now go next
527.53 -> Your value of i has become 1
529.593 -> and 1 has been put on 4
531.213 -> On 4 we will see GHI is there
533.146 -> i == n didn't happened
535.602 -> So it will not go in the if
536.673 -> Here it will check again
538.013 -> keys a of i. A of is is 4
539.761 -> Okay
540.707 -> GHI
541.702 -> GHI's size is also 3
543.133 -> So it will be 3
543.796 -> This will do the same again. it will say helper a,n
546.051 -> We had a in temp
548.133 -> Keys 4,0
550.516 -> What is 4,0
551.805 -> It will say AG
553.248 ->
555.319 -> Do i as +1
557.583 -> When we will +1, it will be 2 in place of 1
561.345 -> And again call the recursion
562.995 -> Then it will call the recursion
564.512 -> It will see that the value of i that has become 2
567.745 -> 2 and 2 became same
569.593 -> So it will go and say add Ag inn the answer
572.159 -> it will add AG in answer
573.586 -> And come back on recursion
576.137 -> It will come back on recursion, so the value in temporary will be A
579.806 -> G will not be there
580.87 -> It will go again
581.841 -> j will be incremented
583.685 -> It will be 1 from 0
585.028 -> After becoming 1 we will see that it is 1 here
587.477 -> AH will come
588.803 -> AH will go above again
590.505 -> Because it will call the recursion
592.978 -> Okay
593.831 -> In this way it will keep calling the recursion
596.092 -> It will come above and call the recursion
597.752 -> Then it will call the recursion
599.088 -> After happening of this, it will call the recursion again above
601.743 -> From where we started
602.756 -> Then it will come on B
604.195 -> It will keep doing the same thing
606.129 -> And in this way all of our possible ways will be generated
609.618 -> And we will get our answer
612.137 -> We have to do nothing
613.747 -> Just go to understand this code
615.676 -> Pick up pen and paper
617.005 -> Try making recursive tree
618.741 -> I have made
622.695 -> We made recursive tree here
624.543 -> Okay
626.12 -> Lets try making it again
627.591 -> Now let me tell it how it will be made
630.529 -> We have 3 options in empty
633.786 -> We said either add a or b or c
637.443 -> Then we said in a
639.224 -> do ag
640.941 -> and ah
641.861 -> and ai
642.659 -> Or do bg, bh, bi
647.795 -> do cg, ch, ci
652.141 -> And these are all our possible outcomes
654.983 -> We will return everything
657.499 -> This is it
658.841 -> It was this much
660.021 -> It looks like a hard question in writing
661.975 -> But very simply from one line of recursion
665.272 -> We did only until one line
666.669 -> We wrote very small code
668.01 -> It is solved
669.248 -> Try solving and if you do not understand anything, do write in the comments section
671.626 -> Lets meet in next video. Till then bye
672.512 ->
Source: https://www.youtube.com/watch?v=MjiQrvblv4k