LeetCode-in-All

76. Minimum Window Substring

Hard

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.

Follow up: Could you find an algorithm that runs in O(m + n) time?

Solution

import "math"

func minWindow(s string, t string) string {
	mapT := make([]int, 128)
	for i := 0; i < len(t); i++ {
		mapT[t[i]-'A']++
	}
	count := len(t)
	begin, end, d, head := 0, 0, math.MaxInt32, 0

	for end < len(s) {
		if mapT[s[end]-'A']--; mapT[s[end]-'A'] >= 0 {
			count--
		}
		end++

		for count == 0 {
			if end-begin < d {
				d = end - begin
				head = begin
			}
			if mapT[s[begin]-'A']++; mapT[s[begin]-'A'] > 0 {
				count++
			}
			begin++
		}
	}

	if d == math.MaxInt32 {
		return ""
	}
	return s[head : head+d]
}

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