// QuickSelect algorithm to find the nth largest element in an unsorted array
// this version have extra memory usage as it does not mutate the original array
int kth_largest(const vector<int> &arr, int k) {
if (k < 0 || k >= arr.size()) return -1;
srand(time_t());
int pivot = arr[rand() % arr.size()];
// partition. Note that we do *not* add pivot into any array
vector<int> L;
vector<int> R;
for (auto x : arr) {
if (x < pivot) {
L.push_back(x);
} else if (x > pivot) {
R.push_back(x);
}
}
// select
if (k + 1 <= L.size()) {
// it's in L
return kth_largest(L, k);
} else if (k + 1 > arr.size() - R.size()) {
// it's in R
return kth_largest(R, k - (arr.size() - R.size()));
} else {
// pivot itself
return pivot;
}
}
int main(void) {
printf("Enter number of elements in max-heap, followed by the max-heap elements, followed by k.\n");
printf("> ");
size_t elems;
while (scanf("%zu", &elems) == 1) {
size_t i;
for (i = 0; i < elems; i++) {
scanf("%d", &input_heap[i]);
}
size_t k;
scanf("%zu", &k);
int res;
if (kth_largest(input_heap, elems, k, &res)) {
printf("%zu-th largest = %d\n", k, res);
} else {
printf("Invalid value of k (%zu)\n", k);
}
printf("> ");
}
return 0;
}
int main()
{
int n;
tree *root = NULL;
while (1) {
scanf("%d", &n);
if (n == -1)
break;
root = insert_BST_iterative(root, n);
}
print_awesome(root);
printf("\n\n");
int k;
scanf("%d", &k);
printf("Kth (%d) Largest Element: %d\n", k, kth_largest(root, k));
cleanup(&root);
return 0;
}
int main(int argc, char const *argv[]) {
vector<vector<int>> arrs {
{1,5, 6, 1,2, 3, 4, 5},
{2, 4, 1,2, 1,1,1, 4, 6},
{8,7,6,5,4,4,3,2,1,},
{1,2,3,4,5,6,7,8},
{1},
};
vector<int> ks {
3,
4,
5,
3,
0,
};
for (int i = 0; i < arrs.size(); ++i) {
cout << "Test : " << kth_largest(arrs[i], ks[i]) << "\n";
nth_element(arrs[i].begin(), arrs[i].begin() + ks[i], arrs[i].end());
cout << "Golden: " << arrs[i][ks[i]] << "\n";
}
return 0;
}
