【Educational Codeforces Round 16】 Codeforces 710E Generate a String

zscoder wants to generate an input file for some programming
competition problem.

His input is a string consisting of n letters ‘a’. He is too lazy to
write a generator so he will manually generate the input in a text
editor.

Initially, the text editor is empty. It takes him x seconds to insert
or delete a letter ‘a’ from the text file and y seconds to copy the
contents of the entire text file, and duplicate it.

zscoder wants to find the minimum amount of time needed for him to
create the input file of exactly n letters ‘a’. Help him to determine
the amount of time needed to generate the input.

Input The only line contains three integers n, x and y (1 ≤ n ≤ 107,
1 ≤ x, y ≤ 109) — the number of letters ‘a’ in the input file and the
parameters from the problem statement.

Output Print the only integer t — the minimum amount of time needed to
generate the input file.

如果没有删除操作比较好想，直接按顺序dp。但是注意到删除操作只会跟在复制之后【因为它不可能跟在添加之后】，删除两次不如之前删除一次。这样就很好枚举了。

#include<iostream>#include<algorithm>using namespace std;long long dp[10000010],x,y;int n;int main(){    int i;    cin>>n>>x>>y;    for (i=1;i<=n;i++)      if (i&1)        dp[i]=min(dp[i-1]+x,min(dp[i/2]+x+y,dp[i/2+1]+x+y));      else        dp[i]=min(dp[i-1]+x,dp[i/2]+y);    cout<<dp[n]<<endl;}