Count Substrings That Differ by One Character LeetCode solution in C++

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class Solution {
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 public:
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  int countSubstrings(string s, string t) {
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    int n = s.size();
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    int m = t.size();
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    int ans = 0;
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    for (int i = 0; i < n; i++) {
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      for (int j = 0; j < m; j++) {
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        int diff = 0;
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        for (int k = 0; i + k < n && j + k < m; k++) {
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          if (s[i + k] != t[j + k]) {
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            diff++;
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          }
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          if (diff > 1) {
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            break;
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          }
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          ans += diff;
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        }
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      }
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    }
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    return ans;
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  }
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};