数据结构--排序

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1 快排

#include <iostream>  using namespace std;int Partition(int a[],int left,int right){if (left<right){int i = left;int j = right;int x = a[i];while (i<j){while (i<j&&a[j]>x)j--;if (i<j) {a[i] = a[j];i++;}while (i<j&&a[i]<x)i++;if (i<j) {a[j] = a[i];j--;}}return i;}}void quick_sort(int a[], int left, int right){if (left < right){int x = a[left];int i = Partition(a, left, right);a[i] = x;quick_sort(a, left, i - 1);quick_sort(a, i + 1, right);}}

2 以O(n)查找a[n]中第k大的元素：

#include<iostream>  #include<stdio.h>  using namespace std;int Partition(int *L, int low, int high){int temp = L[low];int pt = L[low]; //哨兵  while (low != high){while (low < high && L[high] >= pt)high--;L[low] = L[high];while (low < high && L[low] <= pt)low++;L[high] = L[low];}L[low] = temp;return low;}void QSort(int *L, int low, int high)  //快速排序  {int pl;if (low < high){pl = Partition(L, low, high);QSort(L, low, pl - 1);QSort(L, pl + 1, high);}}void findk(int k, int *L, int low, int high){int temp;temp = Partition(L, low, high);if (temp == k - 1){cout << "第" << temp + 1 << "大的数是:" << L[temp] << endl;}else if (temp>k - 1)findk(k, L, low, temp - 1);elsefindk(k, L, temp + 1, high);}int main(){int a[10] = { 15,25,9,48,36,100,58,99,126,5 }, i, j, k;cout << "排序前：" << endl;for (i = 0; i<10; i++) {cout << a[i] << " ";}cout << endl;cout << "请输入你要查找第k大的数：" << endl;cin >> k;findk(k, a, 0, 9); //查找第k大的数不需要全部排序  QSort(a, 0, 9);cout << "排序后：" << endl;for (i = 0; i<10; i++) {cout << a[i] << " ";}cout << endl;system("Pause");return 0;}

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