Building Boxes LeetCode solution in C++

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class Solution {
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 private:
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  int getLayerSize(int x) {
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    return x * (x + 1) / 2;
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  }
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  int getCubeSize(int x) {
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    long d = static_cast<long>(x);
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    long sz = (d * (d + 1) * (d + 2)) / 6;
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    return static_cast<int>(sz);
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  }
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 public:
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  int minimumBoxes(int n) {
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    // First Binary Search
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    int l(0), r(2000), m;
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    while (l <= r) {
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      m = (l + r) / 2;
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      int sz = getCubeSize(m);
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      if (sz <= n)
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        l = m + 1;
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      else
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        r = m - 1;
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    }
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    int aSideOfPyramid = r;
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    int rest = n - getCubeSize(aSideOfPyramid);
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    // Second Binary Search
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    l = 0, r = 2000;
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    while (l <= r) {
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      m = (l + r) / 2;
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      int sz = getLayerSize(m);
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      if (sz < rest)
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        l = m + 1;
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      else
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        r = m - 1;
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    }
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    int addedFloorCubic = l;
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    return getLayerSize(aSideOfPyramid) + addedFloorCubic;
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  }
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};