选择出数列中前k个最大的数。
这里由于数据特殊。所以能够使用hash表的方法：
#include也能够使用选择前k个数，然后排序，只是难度高非常多：#include #include #include using namespace std;const int SIZE = 1000005;const int SMALL = -500000;bool arr[SIZE];int main(){ int n, m, a, maxN = INT_MIN; while (~scanf("%d %d", &n, &m)) { for (int i = 0; i < n; i++) { scanf("%d", &a); arr[a - SMALL] = true; if (a - SMALL > maxN) maxN = a - SMALL; } for (int i = maxN; i >= 0 && m; i--) { if (arr[i]) { if (m > 1) printf("%d ", i + SMALL); else printf("%d\n", i + SMALL); m--; } } } return 0;}
#include#include #include #include using namespace std;int partition(int *arr, int low, int up){ for (int i = low; i < up; i++) if (arr[i] >= arr[up]) swap(arr[low++], arr[i]); swap(arr[low], arr[up]); return low;}//K作为绝对下标位置处理void randSelectK(int *arr, int low, int up, int K){ int r = low + rand() % (up - low + 1); swap(arr[r], arr[up]); int idx = partition(arr, low, up); if (idx > K) randSelectK(arr, low, idx-1, K); else if (idx < K) randSelectK(arr, idx+1, up, K);}void randQuickSort(int *arr, int low, int up){ if (low >= up) return ;//不能是low == up int r = low + rand() % (up - low + 1); swap(arr[r], arr[up]); int mid = partition(arr, low, up); randQuickSort(arr, low, mid-1); randQuickSort(arr, mid+1, up);}const int SIZE = 1000000;int arr[SIZE]; int main(){ int n, m; srand(unsigned(time(NULL))); while(~scanf("%d %d", &n, &m)) { for (int i = 0; i < n; i++) scanf("%d", &arr[i]); randSelectK(arr, 0, n-1, m-1); randQuickSort(arr, 0, m-1); for (int i = 0; i < m-1; i++) { printf("%d ", arr[i]); } printf("%d\n", arr[m-1]); } return 0;}