C++ QuickSorting a vector and keeping the original index numbers -

i have working quicksort function, i'm not sure how retain original index numbers of unsorted data. ideas? thanks! here's function. can incorporate pair in there somehow?

double nearestneighbor::partition(vector<double>& thelist, double start, double end) { int pivot = thelist[end]; int bottom = start - 1; int top = end;  bool notdone = true; while (notdone) {     while (notdone) {         bottom += 1;          if (bottom == top) {             notdone = false;             break;         }         if (thelist[bottom] > pivot) {             thelist[top] = thelist[bottom];             break;         }     }     while (notdone) {         top = top - 1;          if (top == bottom) {             notdone = false;             break;         }         if (thelist[top] < pivot) {             thelist[bottom] = thelist[top];             break;         }     } } thelist[top] = pivot; return top; 

}

//quicksort function

double nearestneighbor::quicksort(vector<double>& thelist, double start, double end) { if (start < end) {     double split = partition(thelist, start, end); //recursion        quicksort(thelist, start, split - 1);     quicksort(thelist, split + 1, end); } else {     return 0; } } 

i have calculated dot product of several vectors , i'm trying print 10 nearest neighbors. can sort them, professor asked return index number of 10 nearest neighbors, i'm trying figure out how retain original index numbers.

for example: sorted data might this:

index number:3 45 15 9 45
data: 10 14 17 30 35

i want print out index numbers. sorry, can't figure out how format numbers line data, think idea.

1. convert std::vector<t> std::vector<std::pair<int, t>>.
2. sort std::vector<std::pair<int, t>> using second of pair.