Find Positive Integer Solution for a Given Equation LeetCode solution in C++

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class Solution {
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 public:
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  vector<vector<int>> findSolution(CustomFunction &customfunction, int z) {
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    int i = 1;
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    vector<vector<int>> ans;
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    // finding minimum i such that there is no x>=i ans y>=i for which f(x,y)=z
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    for (; i < 1001; i++) {
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      if (customfunction.f(i, i) > z) {
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        break;
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      }
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    }
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    i--;
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    int k = i;
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    // checking bottom right grid
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    // k represents x and j represents y
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    for (int j = i; j <= 1000 && k > 0; j++) {
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      int curr = customfunction.f(k, j);
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      if (curr == z) {
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        ans.push_back({k, j});
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        k--;
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      } else if (curr > z) {
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        k--;
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        j--;
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      }
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    }
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    k = i;
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    // checking top left grid
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    // now k represents y and j represents x
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    for (int j = i + 1; j <= 1000 && k > 0; j++) {
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      int curr = customfunction.f(j, k);
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      if (curr == z) {
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        ans.push_back({j, k});
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        k--;
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      } else if (curr > z) {
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        k--;
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        j--;
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      }
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    }
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    return ans;
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  }
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};