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How to Check Palindrome String & Number in Python – GATE, Interview & Placement Practice
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Jun 1, 2025
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0:00
uh hello guys uh welcome to this video
0:02
so in this video I will show you two
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very common programs which is asked
0:06
inside Python
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uh if you go for interview for
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programming or competitive exams such as
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GATE so for placements which is for
0:18
program for palendrome palindrome is
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actually a sequence in which I will show
0:25
you both for strings and numbers
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palendrome is defined as let's suppose I
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take first of all the example of a
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string this is a simple Python program I
0:35
have written whether to detect whether a
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string is palendrome or
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not so if I just execute this program
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here Python app py and it will ask you
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to enter a
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string so it will actually ask you to
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enter a string so if I write here
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t so now what happens if you write TAT
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in the uh same manner T
1:02
A or if you reverse
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it if you just write in the reverse
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order as well it sounds same T A T and T
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A T so you will see this string is a
1:16
palindrome so the sequence remains the
1:20
same here so if I go from this location
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TAT or this location from left to right
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or right to left the sequence remains
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the same so this is actually a
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palendrome string and the example
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suppose I take another example this
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string is not a
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palindrome from uh left to right it
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sounds different from right to left it
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sound
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different from right to left it will m a
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t u a so this is not a palendrome stream
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so this is the program that uh is there
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and now I'll be showing you this program
2:01
step by step inside this Python tutor
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software where it will show you step by
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step how this program execute let me
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paste it here and then click visualize
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executions so first of all it asks you
2:16
to enter a string and we enter a string
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right here let's
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suppose
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T80 once again I write click on submit
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and now you can see the string has been
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stored in a global variable text so this
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variable is
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stored and after that we define a
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variable here is palendrome true so we
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are assuming that the string is a
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palendrome so it's a boolean parameter
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we have declared this variable true now
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for checking this string whether it's a
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palendrome or not we are making use of a
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for loop we click on next so now it
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declares this variable is parentome true
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and now we come to the for loop so for i
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in range and we calculate the length of
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the text which in this case is three
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characters t a t so three characters
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length so the for loop will run
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from we calculate the length of the text
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which is 3 divided by two which will be
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run
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for one time only so it will only run
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for one time because the total length of
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characters is three so 3 divided by two
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comes out to be
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1 so it will only run for one time if I
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go to the for loop so I is equal to zero
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so here we will simply check the very
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first string right here which is t at
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the zero location the string is t so
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right here we check and if it is not
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equal
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to i + 1 so this is negative indexing
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guys in python negative indexing exist
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here you can see we are putting negative
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and i is 0 + 1 so negative-1 so if you
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want to get the rightmost character in
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the string then you write negative -1 so
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this will actually
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uh move to the negative move to the
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rightmost character which is in this
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case is t so in this case t is equal to
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t so this will return true and this will
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not be executed it will come to this
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location
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and if I click next here it will go to
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the next index which is
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a so now the value of so it will
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basically become one so it will not it
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will come out of this loop and this
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condition will is palendrome is true so
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it's already true so now it will print
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out that uh your the string is a
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palindrome so in this easy way you can
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check out basically what we done in this
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we are using negative index right here
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so this
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actually can so if you have a string t a
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t so this negative one that you are
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seeing right here it is accessing to the
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rightmost character so -1 this is this
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is -2 this is
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-3 so negative indexing does exist in
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python so that's why it becomes easy to
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get the rightmost character so we are
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comparing the first character with the
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last character if it's equal to then
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it's a palindrome string because the
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length is only three characters so in
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this case it becomes really easy so
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essentially this is the logic which is
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we are applying in the for loop we are
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running this and we are comparing the
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first character with the rightmost
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character for this we are using negative
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indexing that's all so this is
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the logic for palentum string now we
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come to the number number is also very
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easy so if I run this program
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now so I say Python app 6 so number
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again it's the same if I say 1 to 1
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again it's a palendrome number because
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if you write from left to right it's the
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same if you write from right to left
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it's also same so it's a palendrome
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number so this number is a palendrome if
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I write any other number which sounds
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different let's suppose
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345 so this number is not a palent
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because from right to left it is 5
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43 so now we come to the program so
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essentially we just need to check if the
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reverse of the number is also equal to
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the original number if it's the case
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then we are putting this so now we
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actually first of all take the number so
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I say
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1:1 so this number is stored inside this
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global number variable which is 1:1 and
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then we need to check the reverse of
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this number so for calculating the
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reverse we declare one other variable
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which is reverse equal to zero and for
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this we also have the original number
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which one to one so we are taking two
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variables reverse to zero and original 1
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to
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1 so here we are applying the while loop
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so while the number is greater than zero
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in this case the number is 1 to 1 so
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it's greater than zero now to get the
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rightmost
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character we need to divide the number
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by 10 and this is your percentage to get
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the remainder so this will get the last
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digit because you're dividing the number
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by 10 so the remainder will come out to
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be one so it is stored inside this
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digit and then we
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actually reverse is equal to zero so 0 *
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10 comes out to be 0 0 + 1 so with this
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reverse will be 1 and again we divide
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this number 1 to 1 by 10 so now the
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rightmost characters will be removed now
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it becomes 12 again we check 12 is
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greater than zero again we extract this
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rightmost character again we divide this
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by 10 so it stores the remainder then we
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multiply 1 10 and then you can see so it
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becomes 12 now and then again we divide
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the number by 10 so now it becomes
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1 next step again 1 is greater than zero
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again we divide this this time it it
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will the remainder will come come out to
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be 1
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1 multiplied by 10 120 + 1 which will be
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121 so so the reverse is calculated as
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121 so reverse is equal to the original
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so it it will come out of this while
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loop because number is zero now so now
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the original is equal to the reverse so
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that's why this is actually a palendrome
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number so we print out that this number
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is a palent round so very simple here we
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simply are applying the condition for
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calculating the reverse of the number
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for this we are applying these three
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operations in the while loop first of
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all we divide the number we get the
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remainder then we multiply it by 10 and
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add the remainder and then we divide the
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number so we are doing this inside this
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while loop so once we calculate the
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reverse we are comparing in this if
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condition and if the original is equal
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to reverse then this number is a
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palentro so these two programs are asked
9:47
very commonly inside interviews in
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competitive exams for placements in
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programming interviews
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so in this way you can explain it and uh
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thank you very much for watching this
9:58
video and also check out my website
10:00
freemediatools.com
10:02
uh which contains thousands of tools
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