What is the minimum number of parts required to split the sequence S to in order to obtain sequence T?

Suppose a person has a sequence (S) consisting of integer numbers and would like to split the sequence into a
number (possibly one) of continuous parts. For each part independently, I then choose any integer
value and removes all occurrences of this value in the corresponding part (note that there could be
no such occurrences). After that, the person will combine all parts in the same order to achieve a new
sequence (T).
How to find out the minimum number of parts needed to split the sequence in order to achieve this goal .

let n = size of sequence S and m = size of sequence T

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• Constraints:
  1 <= n,m <= 2000

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• Input Format: n m
  Sequence S
  Sequence T

• Output Format: if it is not possible to transform S into T output -1
  otherwise, output min number of parts required.

• Sample Input and Output:

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My Attempt:
I did not understand how Sequence S={4,2,7,2} can be transformed to T = {4,7}. If I followed this procedure by splitting a sequence into parts such as {4} {2} {7} {2} and then iterate from 1st index and then the 2nd index until the end, and if I encounter the same value I delete all of its occurrences. When I do this, I get the sequence {4,2,7} and minpart is just 1.

And, for the sequence {4,7,1,4,1,7,1}, I am able to get {4,7,1} and minparts are 3.

But I do not understand, how both of these sequences: S = {4,2,7,2} and S = {4,7,1,4,1,7,1} can be transformed to the sequence T = {4,7}?