Minimum Window Substring - Leetcode 76 - Python

Minimum Window Substring

Given two strings s and t of lengths m and n respectively, return the minimum window substring of s such that every character in t (including duplicates) is included in the window. If there is no such substring, return the empty string "".

The testcases will be generated such that the answer is unique.

A substring is a contiguous sequence of characters within the string.

Example 1:

Input: s = "ADOBECODEBANC", t = "ABC"
Output: "BANC"
Explanation: The minimum window substring "BANC" includes 'A', 'B', and 'C' from string t.

Example 2:

Input: s = "a", t = "a"
Output: "a"
Explanation: The entire string s is the minimum window.

Example 3:

Input: s = "a", t = "aa"
Output: ""
Explanation: Both 'a's from t must be included in the window.
Since the largest window of s only has one 'a', return empty string.

Constraints:

m == s.length
n == t.length
1 <= m, n <= 105
s and t consist of uppercase and lowercase English letters.

class Solution:

def minWindow(self, s: str, t: str) -> str:

if t == "" : return ""

ct, sw = {}, {}

for c in t:

ct[c] = 1 + ct.get(c,0) #{'A': 1, 'B': 1, 'C': 1}

ardy ,req =0, len(ct)

ans, alen = [-1, -1], float("infinity")

l = 0 #left

#for right

for r in range(len(s)):

c = s[r]

sw[c] = 1 + sw.get(c,0)

if c in ct and sw[c]==ct[c]:

ardy += 1

while ardy == req:

if (r-l+1) < alen :

ans = [l,r]

alen = (r-l+1)

sw[s[l]] -= 1

if s[l] in ct and sw[s[l]] < ct[s[l]]:

ardy -= 1

l += 1

l, r = ans

return s[l:r+1] if alen != float("infinity") else ""

Explaination

Comments

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