2026/04/24

[LeetCode] 76 Minimum Window Substring

Two Pointer

右邊一直走

若達成substring window條件, left再開始走, 直到不構成window

特別情況是, 字元過多的時候, 要允許window內出現次數出現負數

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class Solution {
public:
  string minWindow(string s, string t) {
    std::unordered_map<char, int> chrMap;
    for (char c : t)
      chrMap[c]++;
    
    int ansLeft;
    int ansLen = INT_MAX;
    int cnt = 0;
    int left = 0;
    int right = 0;
    for (; right < s.size(); right++) {
      if (chrMap.count(s[right])) {
        if (chrMap[s[right]] > 0)
          cnt++;
        chrMap[s[right]]--;
      }

      while (cnt == t.size()) {
        if (right - left + 1 < ansLen) {
          ansLeft = left;
          ansLen = right - left + 1;
        }
        if (chrMap.count(s[left])) {
          chrMap[s[left]]++;
          if (chrMap[s[left]] > 0)
            cnt--;
        }
        left++;
      }
    }
    if (ansLen == INT_MAX)
      return "";
    return s.substr(ansLeft, ansLen);
  }
};
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