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Permutation in String

Question​

Given two strings s1 and s2, write a function to check if s2 contains a permutation of s1.

Example 1
Input: s = "ab"
p = "ba"

Output: True

Solution​

all//Permutation in String.py


def permutationInString(str1, str2):
    l1 = len(str1)
    l2 = len(str2)

    # Return False if strings are not of equal
    # length
    if l1 != l2:
        return False

    # Store the frequency of characters of str1 in
    # a dictionary
    freq = {}
    for i in range(l1):
        freq[str1[i]] = freq.get(str1[i], 0) + 1

    # Traverse str2 to check whether all characters
    # of str1 are present in str2 with same frequency
    for i in range(l2):
        if str2[i] not in freq.keys():
            return False
        else:
            freq[str2[i]] = freq.get(str2[i], 0) - 1
            if freq[str2[i]] < 0:
                return False

    return True