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// 215. Kth Largest Element in an Array
#include <stdio.h>
#include <stdlib.h>
/*
* 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
}
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