#include <stdio.h>
void swap(int *a, int *b) {
int temp = *a;
*a = *b;
*b = temp;
}
int quickSelect(int arr[], int left, int right, int k) {
if (left == right) {
return arr[left];
}
int pivotIndex = left + rand() % (right - left + 1);
pivotIndex = partition(arr, left, right, pivotIndex);
if (k == pivotIndex) {
return arr[k];
} else if (k < pivotIndex) {
return quickSelect(arr, left, pivotIndex - 1, k);
} else {
return quickSelect(arr, pivotIndex + 1, right, k);
}
}
int partition(int arr[], int left, int right, int pivotIndex) {
int pivotValue = arr[pivotIndex];
swap(&arr[pivotIndex], &arr[right]);
int storeIndex = left;
for (int i = left; i < right; i++) {
if (arr[i] < pivotValue) {
swap(&arr[i], &arr[storeIndex]);
storeIndex++;
}
}
swap(&arr[storeIndex], &arr[right]);
return storeIndex;
}
int main() {
int arr[] = {3, 7, 2, 1, 8, 6, 5, 4};
int k = 3;
int n = sizeof(arr) / sizeof(arr[0]);
int result = quickSelect(arr, 0, n - 1, n - k);
printf("第 %d 大元素是:%d\n", k, result);
return 0;
}