Maximum Fruits Harvested After at Most K Steps LeetCode solution in C++

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int MX = 2e5 + 2;
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class Solution {
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 public:
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  int maxTotalFruits(vector<vector<int>> &fruits, int startPos, int k) {
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    int i, l, r, ans = 0;
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    startPos++; // incremented positions by one to make calculations easier.
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    vector<int> prefix_sum(MX);
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    for (auto &it : fruits) prefix_sum[it[0] + 1] = it[1];
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    for (i = 1; i < MX; i++) prefix_sum[i] += prefix_sum[i - 1];
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    for (r = startPos; r < MX && r <= startPos + k; r++) {
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      l = min(startPos, startPos - (k - 2 * (r - startPos)));
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      l = max(1, l);
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      ans = max(ans, prefix_sum[r] - prefix_sum[l - 1]);
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    }
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    for (l = startPos; l > 0 && l >= startPos - k; l--) {
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      r = max(startPos, startPos + (k - 2 * (startPos - l)));
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      r = min(MX - 1, r);
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      ans = max(ans, prefix_sum[r] - prefix_sum[l - 1]);
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    }
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    return ans;
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  }
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};