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[Tut] How To Check if One String is a Subsequence of Another?

How To Check if One String is a Subsequence of Another?

## Problem Formulation

Description

Given two strings `str1` and `str2`, check if `str1` is a subsequence of `str2`.

subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., `"ace"` is a subsequence of `"abcde"` while `"aec"` is not).

constraints:

• `0 <= str1.length <= 100`
• `0 <= str2.length <= 104`
• `str1` and `str2` consist only of lowercase English letters.

Example 1:

```Input: str1 = "abc", str2 = "ahbgdc"
Output: true
```

Example 2:

```Input: str1 = "axc", str2 = "ahbgdc"
Output: false```

### Solution

```def isSubSequence(str1, str2): len_str1 = len(str1) len_str2 = len(str2) index_str1 = 0 # Index of str1 index_str2 = 0 # Index of str2 # Traverse both str1 and str2 while index_str1 < len_str1 and index_str2 < len_str2: # Compare current character of str2 with if str1[index_str1] == str2[index_str2]: # If matched, then move to next character in str1 index_str1 = index_str1 + 1 index_str2 = index_str2 + 1 # If all characters of str1 matched, # then j is equal to m return index_str1 == len_str1 val_1 = 'abc'
val_2 = 'ahbgdc'
print(isSubSequence(val_1, val_2))
```

Output:

`True`

Explanation:

• `len_str1` and `len_str2` store the length of `str1` and `str2` respectively.
• `index_str1` and `index_str2` are used to store the indices of each character of `str1` and `str1` respectively.
• The `while` loop is used to traverse through the strings until a match is found or all the indices of str2 have been traversed in case of no match.
• The `if statement` compares the current character of `str1` and `str2`.
• In case a match is found, the index of the next character in `str2` is taken into account.
• The value of `index_str1` is incremented at every iteration to traverse through all the letters available in `str1` until the subsequence is found.
• Finally, if the subsequence was found the value stored by `index_str1` will be equal to the length of `str1`.

Dry Run:

The following table illustrates the operation at each iteration within the while loop until the match is found.

### Video Solution

The post How To Check if One String is a Subsequence of Another? first appeared on Finxter.

https://www.sickgaming.net/blog/2021/04/...f-another/

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