2026/05/25

[LeetCode] 438 Find All Anagrams in a String

用 "==" 直接比較兩個std::unordered_map是否相同
要小心有插入過但又歸零的key
跟從沒插入過是不等價的
所以要檢查是否有在pattern字串裡
才能插入std::unordered_map

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class Solution {
public:
  vector<int> findAnagrams(string s, string p) {
    if (p.size() > s.size())
      return vector<int>();

    unordered_map<char, int> patMap;
    unordered_map<char, int> curMap;
    vector<int> ans;

    for (int i = 0; i < p.size(); i++)
      patMap[p[i]]++;

    for (int i = 0; i < p.size(); i++)
      if (patMap.count(s[i]))
        curMap[s[i]]++;

    if (patMap == curMap)
      ans.push_back(0);

    for (int left = 0, right = p.size(); right < s.size(); left++, right++) {
      if (patMap.count(s[left]))
        curMap[s[left]]--;
      if (patMap.count(s[right]))
        curMap[s[right]]++;
      if (curMap == patMap)
        ans.push_back(left + 1);
    }
    return ans;
  }
};
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