2024-02-04 Daily Challenge

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In: DailyChallenge
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Today I have done leetcode's February LeetCoding Challenge with cpp.

February LeetCoding Challenge 4

Description

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.

 

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

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
  int cnt[128] = {};
public:
  string minWindow(string s, string t) {
    int chars = 0;
    for(auto c : t) {
      chars += !cnt[c];
      cnt[c] += 1;
    }
    int end = 0;
    int sLen = s.length();
    while(end < sLen && chars) {
      cnt[s[end]] -= 1;
      chars -= !cnt[s[end]];
      end += 1;
    }
    if(chars) return "";
    int resultLen = INT_MAX;
    int resultBegin = 0;
    for(int begin = 0; begin < end; ++begin) {
      if(end - begin < resultLen) {
        resultLen = end - begin;
        resultBegin = begin;
      }
      cnt[s[begin]] += 1;
      while(end < sLen && cnt[s[begin]] > 0) {
        cnt[s[end]] -= 1;
        end += 1;
      }
      if(cnt[s[begin]] > 0) break;
    }
    return s.substr(resultBegin, resultLen);
  }
};

// Accepted
// 266/266 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 80.15 % of cpp submissions (7.7 MB)
Algorithm