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Python: Find the minimum window in a given string which will contain all the characters of another given string

Python String: Exercise-74 with Solution

Write a Python program to find the minimum window in a given string which will contain all the characters of another given string.

Example 1
Input
str1 = " PRWSOERIUSFK "
str2 = " OSU "
Output:
Minimum window is "OERIUS"

Sample Solution:

Python Code:

import collections
def min_window(str1, str2):
    result_char, missing_char = collections.Counter(str2), len(str2)
    i = p = q = 0
    for j, c in enumerate(str1, 1):
        missing_char -= result_char[c] > 0
        result_char[c] -= 1
        if not missing_char:
            while i < q and result_char[str1[i]] < 0:
                result_char[str1[i]] += 1
                i += 1
            if not q or j - i <= q - p:
                p, q = i, j
    return str1[p:q]
           
str1 = "PRWSOERIUSFK"
str2 = "OSU"
print("Original Strings:\n",str1,"\n",str2)
print("Minimum window:")
print(min_window(str1,str2))

Sample Output:

Original Strings:
 PRWSOERIUSFK 
 OSU
Minimum window:
OERIUS

Pictorial Presentation:

Python String: Find the minimum window in a given string which will contain all the characters of another given string.

Flowchart:

Flowchart: Find the minimum window in a given string which will contain all the characters of another given string

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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