﻿ Python: Count number of substrings from a given string of lowercase alphabets with exactly k distinct characters - w3resource

# Python: Count number of substrings from a given string of lowercase alphabets with exactly k distinct characters

## Python String: Exercise-76 with Solution

Write a Python program to count number of substrings from a given string of lowercase alphabets with exactly k distinct (given) characters.

Sample Solution:-

Python Code:

``````def count_k_dist(str1, k):
str_len = len(str1)

result = 0

ctr = [0] * 27

for i in range(0, str_len):
dist_ctr = 0

ctr = [0] * 27

for j in range(i, str_len):

if(ctr[ord(str1[j]) - 97] == 0):
dist_ctr += 1

ctr[ord(str1[j]) - 97] += 1

if(dist_ctr == k):
result += 1
if(dist_ctr > k):
break

return result

str1 = input("Input a string (lowercase alphabets):")
k = int(input("Input k: "))
print("Number of substrings with exactly", k, "distinct characters : ", end = "")
print(count_k_dist(str1, k))
```
```

Sample Output:

```Input a string (lowercase alphabets): wolf
Input k:  4
Number of substrings with exactly 4 distinct characters : 1
```

Flowchart:

## Visualize Python code execution:

The following tool visualize what the computer is doing step-by-step as it executes the said program:

Python Code Editor:

Have another way to solve this solution? Contribute your code (and comments) through Disqus.

What is the difficulty level of this exercise?

Test your Programming skills with w3resource's quiz.

﻿

## Python: Tips of the Day

Check if a given key already exists in a dictionary:

In is the intended way to test for the existence of a key in a dict.

```d = {"key1": 10, "key2": 23}

if "key1" in d:
print("this will execute")

if "nonexistent key" in d:
print("this will not")
```

If you wanted a default, you can always use dict.get():

```d = dict()

for i in range(100):
key = i % 10
d[key] = d.get(key, 0) + 1
```

and if you wanted to always ensure a default value for any key you can either use dict.setdefault() repeatedly or defaultdict from the collections module, like so:

```from collections import defaultdict

d = defaultdict(int)

for i in range(100):
d[i % 10] += 1
```

but in general, the in keyword is the best way to do it.

Ref: https://bit.ly/2XPMRyz