Minimum Window Substring LeetCode solution in C++

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class Solution {
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 public:
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  string minWindow(string s, string t) {
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    unordered_map<char, int> ump;
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    for (auto i : t) {
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      ump[i]++;
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    }
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    int i = 0, j = 0, count = 0;
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    int ans = INT_MAX, answer = 0;
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    for (; j < s.size(); j++) {
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      if (ump[s[j]] > 0) {
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        count++;
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      }
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      ump[s[j]]--;
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      if (count == t.size()) {
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        while (i < j && ump[s[i]] < 0) {
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          ump[s[i]]++;
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          i++;
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        }
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        if (ans > j - i + 1) {
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          ans = j - i + 1;
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          answer = i;
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        }
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        ump[s[i]]++;
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        i++;
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        count--;
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      }
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    }
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    return ans == INT_MAX ? "" : s.substr(answer, ans);
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  }
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};