题目链接: https://www.acwing.com/problem/content/description/1534/

方法一:暴力(能过13/15个数据)

#include<iostream>
#include<algorithm>

using namespace std;

const int N = 100010;

int n,m;
int a[N];

int main()
{
    cin>>n>>m;
    for(int i = 0;i<n;i++) cin>>a[i];
    sort(a,a+n);
    for(int i = 0;i<n;i++)
     for(int j = i + 1;j<n;j++)
     {
         if(a[i] + a[j] == m)
         {
          cout<<a[i]<<' '<<a[j]<<endl;
          return 0;
         }
     }
     cout<<"No Solution"<<endl;
     return 0;
}

方法二:双指针扫描(一前一后扫描，减少时间复杂度)

#include<iostream>
#include<algorithm>

using namespace std;

const int N = 100010;

int n,m;
int a[N];

int main()
{
    cin>>n>>m;
    for(int i = 0;i<n;i++) cin>>a[i];
    sort(a,a+n);
    for(int i = 0;i<n;)
     for(int j = n-1;j > i;)
     {
         if(i < j)
         {
          if(a[i] + a[j] > m) j--;
          if(a[i] + a[j] < m) i++;
         }
         if(a[i] + a[j] == m && i != j)
         {
          cout<<a[i]<<' '<<a[j]<<endl;
          return 0;
         }
         if(i == j) 
         {
             cout<<"No Solution"<<endl;
             return 0;
         }
     }
     return 0;
}