Find the first non repeating character in a string

Published: 22 July 2024
on channel: pythonbuzz
243
like

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=====================================================

from collections import Counter

s = "swiss"
char_count = Counter(s)

for char in s:
if char_count[char] == 1:
print("First non-repeating character:", char)
break

let's break down the code step-by-step:

1. **Import the Counter class from the collections module**:
```python
from collections import Counter
```
The `Counter` class is part of the `collections` module and is used to count the occurrences of elements in an iterable (like a string, list, etc.).

2. **Define the string `s`**:
```python
s = "swiss"
```
Here, we have a string `s` with the value `"swiss"`.

3. **Create a Counter object to count character occurrences**:
```python
char_count = Counter(s)
```
`Counter(s)` creates a dictionary-like object where keys are characters from the string `s` and values are their counts. For the string `"swiss"`, `char_count` will be `Counter({'s': 3, 'w': 1, 'i': 1})`.

4. **Iterate over each character in the string `s`**:
```python
for char in s:
```
This loop goes through each character in the string `s`.

5. **Check if the character occurs only once**:
```python
if char_count[char] == 1:
```
Inside the loop, this condition checks if the current character `char` appears only once in the string `s` by looking it up in the `char_count` dictionary.

6. **Print the first non-repeating character and break the loop**:
```python
print("First non-repeating character:", char)
break
```
If the condition is true (i.e., the character count is 1), it prints the character and immediately exits the loop with the `break` statement. This ensures that only the first non-repeating character is printed.

Putting it all together, the code counts the occurrences of each character in the string `s`, then iterates through the string to find and print the first character that occurs only once. For the string `"swiss"`, the first non-repeating character is `"w"`, so the output will be:

```
First non-repeating character: w
```


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