额…没审好题,没看到没有重复的数字,没想到用哈希,也没想到用Sn求
#include <iostream>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long LL;
int n,x;
int main()
{
cin >> n;
LL sum=(n+1LL)*n/2;
for (int i = 1; i < n; i ++ ){
scanf("%d", &x);
sum-=x;
}
cout << sum;
return 0;
}
暴力做法
#include<bits/stdc++.h>
using namespace std;
const int N = 1e6+10;
int a[N],i,n;
int main()
{
cin>>n;
for(i=1;i<=n;i++)cin>>a[i];
sort(a+1,a+1+n);
for(i=1;i<=n;i++)
if(a[i]+1!=a[i+1]){
cout<<a[i]+1;
return 0;
}
}