Codeforces 623B Array GCD
最后的序列里肯定有a[1], a[1]-1, a[1]+1, a[n], a[n]-1, a[n]+1中的一个,枚举质因子, dp去check
#include<bits/stdc++.h> #define LL long long #define fi first #define se second #define mk make_pair #define PLL pair<LL, LL> #define PLI pair<LL, int> #define PII pair<int, int> #define SZ(x) ((int)x.size()) #define ull unsigned long long using namespace std; const int N = 1e6 + 7; const int inf = 0x3f3f3f3f; const LL INF = 0x3f3f3f3f3f3f3f3f; const int mod = 1e9 + 7; const double eps = 1e-8; LL n, a, b, tot, ans = INF; LL c[N], fac[100], dp[N][3]; void solve(int x) { for(int i = 2; i * i < x; i++) { if(x % i) continue; fac[tot++] = i; while(x % i == 0) x /= i; } if(x > 1) fac[tot++] = x; sort(fac, fac + tot); tot = unique(fac, fac + tot) - fac; } void calc(int fac) { memset(dp, INF, sizeof(dp)); dp[0][0] = 0; for(int i = 0, r1, r2, r3; i < n; i++) { r1 = (c[i + 1] - 1) % fac; r2 = r1 + 1; if(r2 >= fac) r2 -= fac; r3 = r2 + 1; if(r3 >= fac) r3 -= fac; if(dp[i][0] < INF) { dp[i + 1][1] = min(dp[i + 1][1], dp[i][0] + a); if(!r2) dp[i + 1][0] = min(dp[i + 1][0], dp[i][0]); else if(!r1 || !r3) dp[i + 1][0] = min(dp[i + 1][0], dp[i][0] + b); } if(dp[i][1] < INF) { dp[i + 1][1] = min(dp[i + 1][1], dp[i][1] + a); if(!r2) dp[i + 1][2] = min(dp[i + 1][2], dp[i][1]); else if(!r1 || !r3) dp[i + 1][2] = min(dp[i + 1][2], dp[i][1] + b); } if(dp[i][2] < INF) { if(!r2) dp[i + 1][2] = min(dp[i + 1][2], dp[i][2]); else if(!r1 || !r3) dp[i + 1][2] = min(dp[i + 1][2], dp[i][2] + b); } } for(int i = 0; i < 3; i++) ans = min(ans, dp[n][i]); } int main() { scanf("%lld%lld%lld", &n, &a, &b); for(int i = 1; i <= n; i++) scanf("%lld", &c[i]); for(int i = -1; i <= 1; i++) solve(c[1] + i); for(int i = -1; i <= 1; i++) solve(c[n] + i); for(int i = 0; i < tot; i++) calc(fac[i]); printf("%lld\n", ans); return 0; } /* */