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