// 215. Kth Largest Element in an Array #include #include /* * given an integer array 'nums' and an integer 'k', return the k'th largest * element in the array. note that it is the k'th largest elemented in sorted * order, not the k'th distinct element. can you solve without sorting? */ int max(int *a, int n, int i, int j, int k) { int m = i; if (j < n && a[j] > a[m]) m = j; if (k < n && a[k] > a[m]) m = k; return m; } void down_heap(int *a, int n, int i) { while (1) { int j = max(a, n, i, 2 * i + 1, 2 * i + 2); if (j == i) break; int t = a[i]; a[i] = a[j]; a[j] = t; i = j; } } void heapsort(int *a, int n) { for (int i = (n - 2) / 2; i >= 0; i--) down_heap(a, n, i); for (int i = 0; i < n; i++) { int t = a[n - i - 1]; a[n - i - 1] = a[0]; a[0] = t; down_heap(a, n - i - 1, 0); } } int findKthLargest(int *nums, int nums_size, int k) { if (!nums_size || k > nums_size) return 0; heapsort(nums, nums_size); return nums[nums_size - k]; } int main() { int n1[] = {3, 2, 1, 5, 6, 4}, n2[] = {3, 2, 3, 1, 2, 4, 5, 5, 6}; printf("%d\n", findKthLargest(n1, 6, 2)); // expect: 5 printf("%d\n", findKthLargest(n2, 9, 4)); // expect: 4 }