LeetCode in Net

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

public class Solution {
    public string MinWindow(string s, string t) {
        int[] map = new int[128];
        foreach (char c in t) {
            map[c - 'A']++;
        }
        int count = t.Length;
        int begin = 0;
        int end = 0;
        int d = int.MaxValue;
        int head = 0;
        while (end < s.Length) {
            if (map[s[end++] - 'A']-- > 0) {
                count--;
            }
            while (count == 0) {
                if (end - begin < d) {
                    d = end - begin;
                    head = begin;
                }
                if (map[s[begin++] - 'A']++ == 0) {
                    count++;
                }
            }
        }
        return d == int.MaxValue ? "" : s.Substring(head, d);
    }
}

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