题目传送门：http://codeforces.com/contest/710/problem/E
官方题解：http://codeforces.com/blog/entry/46761
这题，做法很多:
有简单粗暴型：http://www.cnblogs.com/Coolxxx/p/5797798.html
也有优雅递推型：http://blog.csdn.net/qq_33184171/article/details/52289905
我是第二种，不过第二种有一个东西需要证明：至少存在一组最优解使得-1操作至多连续进行1次
#include<bits/stdc++.h>
#define LL long long
#define abs(x) ((x)>0?(x):-(x))
using namespace std;
const int N = 1e7+9;
int n,x,y;
LL f[N];
inline int read(){
char c=getchar(); int ret=0,f=1;
while (c<'0'||c>'9') {if(c=='-')f=-1;c=getchar();}
while (c<='9'&&c>='0') ret=ret*10+c-'0',c=getchar();
return ret*f;
}
int main(){
n = read(); x = read(); y = read();
f[1] = x; for (int i=2;i<=n;i++) {
f[i] = f[i-1] + x;
if (i & 1) f[i] = min(f[i], f[i+1>>1] + x + y);
else f[i] = min(f[i], f[i>>1] + y);
}
printf("%I64d\n",f[n]);
return 0;
}
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