29.最小的K个数——剑指offer
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,。
1 class Solution {//快速排序nlogn 2 private: 3 int Partion(vector<int> &input,int low,int high) 4 { 5 int i = low; 6 int j = high; 7 int temp = input[low]; 8 while(i < j) 9 { 10 while(i < j && temp <= input[j]) --j; 11 input[i] = input[j]; 12 while(i < j && temp >= input[i]) ++i; 13 input[j] = input[i]; 14 } 15 input[i] = temp; 16 return i; 17 } 18 void quicksort(vector<int> &input ,int low , int high) 19 { 20 if(low < high) 21 { 22 int pivot = Partion(input, low , high); 23 quicksort(input, low, pivot -1); 24 quicksort(input, pivot + 1, high); 25 } 26 } 27 public: 28 vector<int> GetLeastNumbers_Solution(vector<int> input, int k) { 29 int l = input.size(); 30 vector<int> res; 31 if(l < k) return res; 32 quicksort(input, 0 , l - 1); 33 for(int i = 0; i < k; ++i) 34 { 35 res.push_back(input[i]); 36 } 37 return res; 38 } 39 };
1 class Solution {//堆排序时间复杂度nlogk 2 private: 3 void heapsort(vector<int> &input , int k) 4 { 5 for(int i = k/2 - 1; i >= 0; --i) 6 { 7 int j = 2*i + 1; //左结点 8 while(j < k) 9 { 10 if(j < k - 1 &&input[j + 1] > input[j]) j++; 11 if(input[i] >= input[j]) break; 12 else swap(input[j], input[i]); 13 } 14 } 15 } 16 public: 17 vector<int> GetLeastNumbers_Solution(vector<int> input, int k) { 18 int n = input.size(); 19 vector<int> res; 20 if(n < k) return res; 21 heapsort(input, k); 22 for(int i = k; i < n; ++i) 23 { 24 if(input[i] < input[0]) 25 { 26 swap(input[0], input[i]); 27 heapsort(input, k); 28 } 29 } 30 for(int i = 0; i < k; ++i) 31 { 32 res.push_back(input[i]); 33 } 34 return res; 35 } 36 };
