codeforces 891A Pride (数学）

题目链接：https://codeforces.com/problemset/problem/891/A

如果原序列有 1 ，答案等于 n 减一的个数
没有 1 ，则找出公约数最短的序列长度

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<cmath>
#include<stack>
#include<queue>
using namespace std;
typedef long long ll;

const int maxn = 2010;

int n;
int a[maxn],dp[maxn][maxn],g[maxn][maxn];

int gcd(int a,int b){ return b==0?a:gcd(b,a%b); }

ll read(){ ll s=0,f=1; char ch=getchar(); while(ch<'0' || ch>'9'){ if(ch=='-') f=-1; ch=getchar(); } while(ch>='0' && ch<='9'){ s=s*10+ch-'0'; ch=getchar(); } return s*f; }

int main(){
	n = read();
	
	int mi = 1000000007;
	
	int f=0;
	for(int i=1;i<=n;++i){
		a[i] = read(), g[i][i] = a[i];
		if(g[i][i] == 1){
			++f;
			mi = 0;
		}
	}
	
	for(int l=2;l<=n;++l){
		for(int i=1;i<=n;++i){
			int r = min(n,i+l-1);
			g[i][r] = gcd(g[i][r-1],a[r]);
			if(g[i][r] == 1){
				mi = min(mi,l-1);
			}
		}
	}
	
	if(mi == 1000000007){
		printf("-1\n");
	}
	else if(f>0){
		printf("%d\n",n-f);
	}
	else{
		printf("%d\n",mi + n - 1);
	}
	 
	return 0;
}