【剑指offer】题目1371：最小的K个数

题目描述：

输入n个整数，找出其中最小的K个数。例如输入4,5,1,6,2,7,3,8这8个数字，则最小的4个数字是1,2,3,4,。

输入：

每个测试案例包括2行：

第一行为2个整数n，k(1<=n，k<=200000)，表示数组的长度。

第二行包含n个整数，表示这n个数，数组中的数的范围是[0,1000 000 000]。

输出：

对应每个测试案例，输出最小的k个数，并按从小到大顺序打印。

样例输入：

8 44 5 1 6 2 7 3 8

样例输出：

1 2 3 4

基于快速排序划分的思路，平均时间复杂度O（n）

#include <iostream>#include <string>#include <cstdio>#include <cstdlib>#include <algorithm>void swap(int *a, int *b){int tmp = *a;*a = *b;*b = tmp;}int Partition(int data[],int length, int lhs, int rhs){if (data == NULL || length <= 0 || lhs < 0 || rhs >= length){return -1;}int pivot = data[rhs];int small = lhs - 1;for (int i = lhs; i < rhs; i++){if (data[i] < pivot){small++;if (small != i){swap(&data[i], &data[small]);}}}small++;swap(&data[small], &data[rhs]);return small;}void GetleastKnumber(int *data, int n, int k){if (data == NULL || n <= 0 || k <= 0){return;}if (k >= n){std::sort(data, data+n);for (int i = 0; i < n; i++){if (i > 0){printf(" ");}printf("%d", data[i]);}printf("\n");return ;}int lhs = 0, rhs = n-1;int index = Partition(data, n, lhs, rhs);while(k-1 != index){if (k-1 < index){rhs = index -1;index = Partition(data, n, lhs, rhs);}else{lhs = index + 1;index = Partition(data, n, lhs, rhs);}}std::sort(data, data+k);for (int i = 0; i < k; i++){if (i > 0){printf(" ");}printf("%d", data[i]);}printf("\n");return ;}int GetKthSmallNum(int *data, int n, int k){return 0;}int main(){int n, k;while(scanf("%d %d", &n, &k) != EOF){int *data = new int[n];if (data == NULL){break;}for (int i = 0; i < n; i++){scanf("%d", &data[i]);}GetleastKnumber(data, n, k);delete[] data;}//system("pause");return 0;}

#include <iostream>#include <string>#include <cstdio>#include <cstdlib>#include <algorithm>void swap(int *a, int *b){int tmp = *a;*a = *b;*b = tmp;}int Partition(int data[],int length, int lhs, int rhs){if (data == NULL || length <= 0 || lhs < 0 || rhs >= length){return -1;}int pivot = data[rhs];int small = lhs - 1;for (int i = lhs; i < rhs; i++){if (data[i] < pivot){small++;if (small != i){swap(&data[i], &data[small]);}}}small++;swap(&data[small], &data[rhs]);return small;}void GetleastKnumber(int *data, int n, int k){if (data == NULL || n <= 0 || k <= 0){return;}if (k >= n){std::sort(data, data+n);for (int i = 0; i < n; i++){if (i > 0){printf(" ");}printf("%d", data[i]);}printf("\n");return ;}int lhs = 0, rhs = n-1;int index = Partition(data, n, lhs, rhs);while(k-1 != index){if (k-1 < index){rhs = index -1;index = Partition(data, n, lhs, rhs);}else{lhs = index + 1;index = Partition(data, n, lhs, rhs);}}std::sort(data, data+k);for (int i = 0; i < k; i++){if (i > 0){printf(" ");}printf("%d", data[i]);}printf("\n");return ;}int GetKthSmallNum(int *data, int n, int k)// 函数返回第K小的数{if (data == NULL || k > n){return -1;}int lhs = 0, rhs = n-1;int index = Partition(data, n, lhs, rhs);while(index != k-1){if(k-1 < index){rhs = index -1;index = Partition(data, n, lhs , rhs);}else{lhs = index + 1;index = Partition(data, n, lhs , rhs);}}return data[index];}int main(){int n, k;while(scanf("%d %d", &n, &k) != EOF){int *data = new int[n];if (data == NULL){break;}for (int i = 0; i < n; i++){scanf("%d", &data[i]);}//GetleastKnumber(data, n, k);GetKthSmallNum(data, n, k);delete[] data;}//system("pause");return 0;}