Codeforces Round #691 (Div. 2)A-C题
Div2第一次AC两道题
A题：
直接比较一张卡片上的两个数，blue大blue ,red大red ，最后比较（当时就凭感觉应该是这样qwq）
#include<iostream>#include<stdio.h>#include<string>#include<algorithm>using namespace std;char r[1005];char b[1005];int main(){ int t; cin>>t; int n; int blue; int red; while(t--){ cin>>n; red = blue = 0; for (int i = 1;i<=n;i ){ cin >> r[i]; } for (int i = 1; i <= n;i ){ cin >> b[i]; } for (int i = 1; i <= n;i ){ if((int)(r[i]-'0')>(int)(b[i]-'0')) red ; if((int)(r[i]-'0')<(int)(b[i]-'0')) blue ; } if (red > blue) cout<<"RED"<<endl; if(red<blue) cout << "BLUE" << endl; if(red==blue) cout << "EQUAL" << endl; } return 0;}
一开始用dfs搜，明显超时，果断用dfs找规律
#include<iostream>using namespace std;//dfs打表wow//前面是dfs搜的代码/*void dfs(int x,int y){ if(num==n){ if(!vis[x][y]){ vis[x][y] = 1; sum ; } return; } for (int i = 1;i<=2;i ){ if (flag) { num ; flag = 0; dfs(x 1, y); num--; num ; flag = 0; dfs(x - 1, y); num--; return; } else { num ; flag = 1; dfs(x, y 1); num--; num ; flag = 1; dfs(x, y - 1); num--; return; } }}int main(){ cin>>n; flag = 0; dfs(500,500); long long k=sum; cout << sum << endl; flag = 1; dfs(500, 500); cout<<sum-k<<endl; cout << sum; return 0;}*/int main(){ int n; cin >> n; if(n%2==0){ cout << (n / 2 1) * (n / 2 1); return 0; }else{ n ; cout << ((n / 2 1) * (n / 2 1) - (n / 2 1))*2; return 0; }}
C题：（补题）
比赛时没做出来（其实是不会）
（数论一直搞不懂）
gcd(a,b)=gcd(a-b,b)
#include<iostream>#include<stdio.h>#include<algorithm>using namespace std;long long gcd(long long x,long long y){ if(y==0) return x; else return gcd(y, x % y);}long long a[200006];int main(){ int n; int m; long long t; long long gcd_x=1; cin >> n >> m; for(int i=1;i<=n;i ) cin>>a[i]; sort(a 1, a n 1); if(n>=2){ gcd_x = a[2] - a[1]; for (int i = 3; i <= n;i ) gcd_x=gcd(gcd_x,a[i]-a[i-1]); for (int i = 1;i<=m;i ){ cin>>t; cout << gcd(gcd_x, a[1] t) << ' '; } }else{ for (int i = 1; i <= m;i ){ cin >> t; cout << t a[1] << ' '; } } return 0;}
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