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要想了解更多关于lower_bound/upper_bound -> 【C++函数速查】lower_bound和upper_bound使用方法详细解读

Vector版

#include<bits/stdc++.h>
#define ULL unsigned long long
#define LL long long
#define endl '\n'
#define debug(a) cout<<#a<<"="<<a<<endl;
#define PII pair<int,int>
using namespace std;
const int N =  1 *1e7 + 10,M = 5 * 1e3 + 10,inf = 0x3f3f3f3f;
int n,m;
int find(int x,vector<int> a)
{
    return lower_bound(a.begin(),a.end(),x) - a.begin();
}
void solve()
{
    cin>>n;
    vector<int> arr(n);
    for(int i=0;i<n;i++) cin>>arr[i];
    cin>>m;
    sort(arr.begin(),arr.end());
    // 1 2 4 5
    for(auto x : arr)
    {
        int t = m - x; //求出要找出的数
        int i = find(t,arr); //找到第一个大于等于t的下标
        if(arr[i] == t && arr[i] != x) //该下标的数是等于t并且不是自己
        {
            cout<<x<<' '<<t;
            exit(0);
        }
    }
    cout<<"No"<<endl;
}
int main()
{
    ios::sync_with_stdio(0);cin.tie(nullptr),cout.tie(0);
    int _=1;
    // cin>>_;
    while(_--)
    {
        solve();
    }
    return 0;
}
/**
 *    author: Nijika_jia
 *    created: 2024.10.12 23:02:03
 */

常规数组版

#include<bits/stdc++.h>
#define ULL unsigned long long
#define LL long long
#define endl '\n'
#define debug(a) cout<<#a<<"="<<a<<endl;
#define PII pair<int,int>
using namespace std;
const int N =  1 *1e7 + 10,M = 5 * 1e3 + 10,inf = 0x3f3f3f3f;
int n,m;
int arr[N];
int find(int x,int a[])
{
    return lower_bound(a,a+n,x) - a;
}
void solve()
{
    cin>>n;
    for(int i=0;i<n;i++) cin>>arr[i];
    cin>>m;
    // 1 2 4 5
    sort(arr,arr+n);
    for(int i=0;i<n;i++)
    {
        int t = m - arr[i]; //求出要找出的数
        int j = find(t,arr); //找到第一个大于等于t的下标
        if(arr[j] == t && arr[j] != arr[i]) //该下标的数是等于t并且不是自己
        {
            cout<<arr[i]<<' '<<t;
            exit(0);
        }
    }
    cout<<"No"<<endl;
}
int main()
{
    ios::sync_with_stdio(0);cin.tie(nullptr),cout.tie(0);
    int _=1;
    // cin>>_;
    while(_--)
    {
        solve();
    }
    return 0;
}
/**
 *    author: Nijika_jia
 *    created: 2024.10.12 23:02:03
 */

手写二分版

#include<bits/stdc++.h>
#define ULL unsigned long long
#define LL long long
#define endl '\n'
#define debug(a) cout<<#a<<"="<<a<<endl;
#define all(v) v.begin(), v.end()
#define PII pair<int,int>
using namespace std;
const int N =  1 *1e6 + 10,M = 5 * 1e3 + 10,inf = 0x3f3f3f3f;
int n,m;
int a[N];
int find(int x)
{
    int l = 0 , r = n;
    while (l < r)
    {
        int mid = l + r >> 1;
        if(a[mid] == x) return mid;
        if(a[mid] < x) l = mid+1;
        else r = mid;
    }
    return l;
}
void solve()
{
    cin>>n;
    for(int i=0;i<n;i++) cin>>a[i];
    cin>>m;
    sort(a,a+n);
    for(int i=0;i<n;i++)
    {
        int t = m - a[i];
        int j = find(t);
        if(a[j] != a[i] &&  a[j] == t)
        {
            cout<<a[i]<<' '<<a[j];
            exit(0);
        }
    }
    cout<<"No"<<endl;
}
int main()
{
    ios::sync_with_stdio(0);cin.tie(nullptr),cout.tie(nullptr);
    int _=1;
    // cin>>_;
    while(_--)
    {
        solve();
    }
    return 0;
}
/**
 *    author: Nijika_jia
 *    created: 2024.10.16 22:52:32
 */