快排模板

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#include<iostream>
using namespace std;

const int N=1E6+10;
int n,q[N];

void quick_sort(int q[],int l,int r){
    if(l>=r) return;
    
    int x=q[(l+r)/2],i=l-1,j=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(){
    scanf("%d",&n);
    for(int i=0;i<n;i++) scanf("%d",&q[i]);
    
    quick_sort(q,0,n-1);
    
    for(int i=0;i<n;i++) printf("%d ",q[i]);
    
    return 0;
}
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#include<iostream>
#include<algorithm>
using namespace std;

const int N = 1e6+10;
int n, k;
int q[N];

int quick_sort(int l, int r, int k) {
    if (l == r) return q[l];
    

    int x = q[(l + r) / 2], i = l - 1, j = 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]);
    }
    
    int s1 = j - l + 1;
    if (k <= s1) return quick_sort(l, j, k);
    return quick_sort(j + 1, r, k - s1);

}

int main() {
    cin >> n >> k;

    for (int i = 0; i < n; i++) cin >> q[i];
    
    cout << quick_sort(0, n - 1, k) << endl;
    
    return 0;

}

acw786.第k个数

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#include<iostream>
using namespace std;

const int N=1e6+10;
int n,k;
int q[N];

int main(){
    cin>>n>>k;
    for(int i=0;i<n;i++) scanf("%d",&q[i]);
    while(k--){
        int x;
        cin>>x;
        

        int l=0,r=n-1;
        while(l<r){
            int mid=(l+r)>>1;
            if(q[mid]>=x) r=mid;
            else l=mid+1;
        }
        
        if(q[l]!=x) cout<<"-1 -1"<<endl;
        else{
            cout<<l<<' ';
            int l=0,r=n-1;
            while(l<r){
                int mid=(l+r+1)>>1;
                if(q[mid]<=x) l=mid;
                else r=mid-1;
            }
            cout<<l<<endl;
        }
    }
}

acw.789 数的范围–二分查找

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#include<iostream>
using namespace std;

const int N=1e6+10;
int n,k;
int q[N];

int main(){
    cin>>n>>k;
    for(int i=0;i<n;i++) scanf("%d",&q[i]);
    while(k--){
        int x;
        cin>>x;
        

        int l=0,r=n-1;
        while(l<r){
            int mid=(l+r)>>1;
            if(q[mid]>=x) r=mid;
            else l=mid+1;
        }
        if(q[l]!=x) cout<<"-1 -1"<<endl;
        else{
            cout<<l<<' ';
            int l=0,r=n-1;
            while(l<r){
                int mid=(l+r+1)>>1;
                if(q[mid]<=x) l=mid;
                else r=mid-1;
            }
            cout<<l<<endl;
        }
    }
    return 0;

}