一起学数据结构和算法系列

Posted 2021-04-12 一只计蒜鸡

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快速排序

题目一：

#include <iostream>using namespace std;
const int N = 100010;int q[N];
void quick_sort(int q[], int l, int r){ if(l >= r) return;  int i = l - 1, j = r + 1, x = q[l + r >> 1];  while(i < j) { do i ++; while(q[i] < x); do j --; while(q[j] > x);  if(i < j) swap(q[i], q[j]); }  quick_sort(q, l, j); quick_sort(q, j + 1, r);}int main(){ int n; cin >> n; for(int i = 0; i < n; i ++ ) cin >> q[i];  quick_sort(q, 0, n - 1);  for(int i = 0; i < n; i ++ ) cout << q[i] << " ";  return 0;}

题目二：

#include <iostream>using namespace std;
int n,k;const int N = 100010;int q[N];
int quick_sort(int q[], int l, int r, int k){ if(l == r) return q[l]; int i = l - 1, j = r + 1, x = q[l + r >> 1];  while(i < j) { do i ++; while(q[i] < x); do j ++; while(q[j] > x);  if(i < j) swap(q[i], q[j]); }  if(j - l + 1 > k) return quick_sort(q, l, j, k); else return quick_sort(q, j + 1, r, k - (j - l + 1));}int main(){ cin >> n >> k; for(int i = 0; i < n; i ++ ) cin >> q[i];  cout << quick_sort(q, 0, n-1, k) << endl; }

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