Beautiful Arrangement II LeetCode solution in C++

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class Solution {
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 public:
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  vector<int> constructArray(int n, int k) {
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    int diff = n - k;
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    int lo = 1;
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    int hi = n;
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    vector<int> out;
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    int i = 0;
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    // we generate a difference of 1 between subsequent elements for the first
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    // n-k times.
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    while (i < diff) {
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      out.push_back(lo);
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      lo++;
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      i++;
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    }
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    bool flag = true;
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    // Now we go zig zag to generate k unique differences, the last one will be
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    // automatically taken care as the difference between last two elements will
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    // be one which we have already generated above.
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    for (int i = out.size(); i < n; i++) {
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      // flag to alternatively zig zag
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      if (flag) {
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        out.push_back(hi);
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        hi--;
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        flag = false;
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      } else {
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        out.push_back(lo);
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        lo++;
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        flag = true;
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      }
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    }
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    return out;
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  }
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};