How should I practice Shortest Sequence of Source Subsequences?

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Shortest Sequence of Source Subsequences

Pinterest● MediumFULLTIMEONSITE INTERVIEW

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Problem statement

Form target by concatenating subsequences of source. Return the minimum number of source subsequences required, or -1 when impossible. An empty target requires zero subsequences.

Function

shortestSourceSubsequences(source: String, target: String) → int

Examples

Example 1

source = "abc"target = "abcbc"return = 2

Use abc followed by bc.

Example 2

source = "abc"target = "acdbc"return = -1

The character d never occurs in source.

Example 3

source = "xyz"target = ""return = 0

No subsequence is needed.

Constraints

1 <= source.length <= 10^5.
0 <= target.length <= 10^5.
Both strings contain lowercase English letters.