C排序算法

Posted 2021-12-18 彭祥.

快速排序算法

#include <algorithm>
#include <iostream>
#include <cstdlib>
#include <ctime>
using namespace std;
int a[100005];
void quick_sort(int l,int r)
    if(l>=r)
        return;
    
    int p1=l,p2=r;
    swap(a[l],a[rand()%(r-l+1)+l]);
    int pivot=a[l];
    while(p1<p2)
        while(a[p2]>=pivot&&p1<p2)
            p2--;
        
        while(a[p1]<=pivot&&p1<p2)
            p1++;
        
        if(p1<p2)
            swap(a[p1],a[p2]);
        
    
    swap(a[l],a[p1]);
    quick_sort(l,p1-1);
    quick_sort(p1+1,r);
    

int main() 
    srand(time(NULL));
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) 
        cin >> a[i];
    
    quick_sort(0,n-1);
    for (int i = 0; i < n; i++) 
        cout << a[i] << " ";
    
    return 0;

冒泡排序

#include <algorithm>
#include <iostream>
using namespace std;
int a[1005];
int main() 
    freopen("gravity.in","r",stdin);
    freopen("gravity.out","w",stdout);
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) 
        cin >> a[i];
    
    for(int i=0;i<n-1;i++)
        bool swapped=false;
        for(int j=0;j<n-i-1;j++)
            if(a[j]>a[j+1])
                swap(a[j],a[j+1]);
                swapped=true;
            
        
        if(!swapped)
            break;
        
    
    for (int i = 0; i < n; i++) 
        cout << a[i] << " ";
    
    return 0;

插入排序

#include <iostream>
#include <algorithm>
using namespace std;
int a[1005];
int main() 
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) 
        cin >> a[i];
    
    for(int i=0;i<n;i++)
        for(int j=i;j>=1;j--)
            if(a[j]<a[j-1])
                swap(a[j],a[j-1]);
            else
                break;
            
        
    
    for (int i = 0; i < n; i++) 
        cout << a[i] << " ";
    
    return 0;

选择排序

#include <algorithm>
#include <iostream>
using namespace std;
int a[1005];
int main() 
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) 
        cin >> a[i];
    
    for(int i=0;i<n-1;i++)
        int min_id=i;
        for(int j=i+1;j<n;j++)
            if(a[j]<a[min_id])
                min_id=j;
            
        
        if(i!=min_id)
            swap(a[i],a[min_id]);
        
    
    for (int i = 0; i < n; i++) 
        cout << a[i] << " ";
    
    return 0;

归并排序

#include <iostream>
using namespace std;
int a[100005], b[100005];
void merge(int l, int r) 
    int p1=l,mid=(l+r)/2,p2=mid+1,p=l;
    while(p1<=mid&&p2<=r)
        if(a[p1]<=a[p2])
            b[p++]=a[p1++];
        else
            b[p++]=a[p2++];
        
    
    while(p1<=mid)
        b[p++]=a[p1++];
    
    while(p2<=r)
        b[p++]=a[p2++];
    
    for(int i=l;i<=r;i++)
        a[i]=b[i];
    

void merge_sort(int l, int r) 
    if(l==r)
        return;
    
    int mid=(l+r)/2;
    merge_sort(l,mid);
    merge_sort(mid+1,r);
    merge(l,r);

int main() 
    int n;
    cin >> n;
    for (int i = 0; i < n; i++) 
        cin >> a[i];
    
    merge_sort(0,n-1);
    for (int i = 0; i < n; i++) 
        cout << a[i] << " ";
    
    return 0;