#include<iostream>
using namespace std;
const int N=1e5+1;
int n,x,a[N],k=1;
int main(){
	cin>>n;
	for(int i=1;i<=n;i++)scanf("%d",&a[i]);
	cin>>x;
	for(int i=1;i<=n;i++){
		if(a[i-1]<x&&x<=a[i]){
			cout<<x<<" ";
			k=0;
		}
		cout<<a[i]<<" ";
	}
	if(k)cout<<x;
	return 0;
}

#include <bits/stdc++.h>
using namespace std;
const int N=1e7+10;
const int INF=0x3f3f3f3f;
int a[N],f;
int main()
{
	int n,m;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i];
	}
	cin>>m;
	a[n+1]=m;
	sort(a+1,a+n+2);
	for(int i=1;i<=n+1;i++)
	{
		cout<<a[i]<<" ";
	}
	return 0;
}

最简单题解

插入排序：我懂

#include <bits/stdc++.h>
using namespace std;
const int N=1e7+10;
const int INF=0x3f3f3f3f;
int a[N],f;
int main()
{
	int n,m;
	cin>>n;
	for(int i=1;i<=n;i++)
	{
		cin>>a[i];
	}
	cin>>m;
	for(int i=1;i<=n;i++)
	{
		if((m<=a[i] && f==0))
		{
			cout<<m<<" ";
			f=1;
		}
		cout<<a[i]<<" ";
	} 
	if(f==0)
	{
		cout<<m;
	}
	return 0;
}

#include <iostream>
#include <stack>
#include <cmath>
#include <vector>
#include <string.h>
#include <queue>
#include <stdio.h>
#include <iomanip>
#include <cstdio>
#include <algorithm>
#define int long long
using namespace std;
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
int a[N];
signed main()
{
    int n;
    cin >> n;
    for(int i = 1; i <= n; i++)
    {
        cin >> a[i];
    }
    a[n + 1] = INF;
    a[0] = -INF;
    int x;
    bool flag = 0;
    cin >> x;
    for(int i = 1; i <= n; i++)
    {
        if(x > a[i - 1] && x <= a[i])
        {
            cout << x << " ";
            flag = 1;
        }
        cout << a[i] << " ";
    }
    if(flag == 0)
    {
        cout << x << endl;
    }
	return 0;
}

以一己之力将难度8变成了难度7

#include <iostream>
#include <stack>
#include <cmath>
#include <vector>
#include <string.h>
#include <queue>
#include <stdio.h>
#include <iomanip>
#include <cstdio>
#include <algorithm>
#define int long long
using namespace std;
const int N = 1e5 + 10;
const int INF = 0x3f3f3f3f;
int a[N];
signed main()
{
    int n;
    cin >> n;
    for(int i = 1; i <= n; i++)
    {
        cin >> a[i];
    }
    a[n + 1] = INF;
    a[0] = -INF;
    int x;
    bool flag = 0;
    cin >> x;
    for(int i = 1; i <= n; i++)
    {
        if(x > a[i - 1] && x <= a[i])
        {
            cout << x << " ";
            flag = 1;
        }
        cout << a[i] << " ";
    }
    if(flag == 0)
    {
        cout << x << endl;
    }
	return 0;
}