Longest Substring Without Repeating Characters LeetCode solution in C++

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class Solution {
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 public:
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  int lengthOfLongestSubstring(string s) {
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    map<char, int> mp;
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    int ans = 1;
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    for (auto ch : s) {
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      if (mp.find(ch) != mp.end()) {
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        while (mp.find(ch) != mp.end()) mp.erase(mp.begin());
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      }
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      mp.insert({ch, 1});
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      if (mp.size() > ans) ans = mp.size();
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    }
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    return ans;
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  }
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};