Which XXX completes the C++ Quickselect() function? int Quickselect(int* numbers, int startIndex, int endIndex, int k) { if (startIndex = endIndex) { return numbers[startIndex]; } int lowLastIndex = Partition(numbers, startIndex, endIndex); if (k

Question

Which XXX completes the C++ Quickselect() function?

int Quickselect(int* numbers, int startIndex, int endIndex, int k) {
   if (startIndex >= endIndex) {
      return numbers[startIndex];
   }

int lowLastIndex = Partition(numbers, startIndex, endIndex);
   if (k <= lowLastIndex) {
      return XXX;
   }
   return Quickselect(numbers, lowLastIndex + 1, endIndex, k);
}

BlackTom AI · Accepted Answer

The prompt presents a Quickselect function and asks which XXX completes the recursive call path. Notably, there are no answer options listed to evaluate, so I will reason about the intended control flow.

In Quickselect, after partitioning the array segment [startIndex, endIndex], we obtain a pivot index (lowLastIndex) that partitions the elements such that all elements to the left are less than or equal to the pivot, and all elements to the right are greater.

If k is less than or equal to lowLastIndex, the desired k-th element lies in the left portion, including the pivot position. Therefore, the correct recursive call should constrain the end index to the pivot index, effectively narrowing the search to [startIndex, lowLastIndex]. The appropriate call is Quickselect(numbers, startIndex, lowLastIndex, k).

If k were greater than lowLastIndex, we would search the right portion, hence the existing code uses Quickselect(numbers, lowLastIndex + 1, endIndex, k).

Given these principles, the completion XXX should be the recursive call that searches the left subarray up to lowLastIndex.

Therefore, the correct expression is Quickselect(numbers, startIndex, lowLastIndex, k).

类似问题

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