Can Convert String in K Moves LeetCode solution in C++

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class Solution {
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 public:
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  bool canConvertString(string s, string t, int k) {
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    int m = s.length(), n = t.length(), count = 0;
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    if (m != n) return false;
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    unordered_map<int, int> mp;
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    for (int i = 0; i < m; i++) {
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      if (t[i] == s[i]) continue;
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      int diff = t[i] - s[i] < 0 ? 26 + t[i] - s[i] : t[i] - s[i];
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      if (mp.find(diff) == mp.end()) {
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        count = max(count, diff);
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      } else {
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        count = max(count, (mp[diff] * 26) + diff);
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      }
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      mp[diff]++;
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      if (count > k) return false;
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    }
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    return count <= k;
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  }
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};