LeetCode-in-Cpp

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

#include <string>
#include <vector>
#include <climits>

class Solution {
public:
    std::string minWindow(const std::string& s, const std::string& t) {
        std::vector<int> map(128, 0);
        for (char c : t) {
            map[c]++;
        }
        
        int count = t.size();
        int begin = 0;
        int end = 0;
        int d = INT_MAX;
        int head = 0;

        while (end < s.size()) {
            if (map[s[end++]]-- > 0) {
                count--;
            }
            
            while (count == 0) {
                if (end - begin < d) {
                    d = end - begin;
                    head = begin;
                }
                if (map[s[begin++]]++ == 0) {
                    count++;
                }
            }
        }

        return d == INT_MAX ? "" : s.substr(head, d);
    }
};

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