codeforces 909C. Python Indentation

动态规划的题目

状态转移方程参考https://www.cnblogs.com/Leohh/p/8135525.html

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<string>
#include<vector>
#define DEBUG(x) cout<<#x<<" = "<<x<<endl
using namespace std;
const int MAXN=5e3+10;
const int MOD=1e9+7;
///第i个表达式缩进j个单位，有多少种结果
int dp[MAXN][MAXN];
char prg[MAXN];
int main()
{
//    freopen("in.txt","r",stdin);
    int n;
    scanf("%d
",&n);
    for(int i=1;i<=n ;i++ ){
        scanf("%c
",&prg[i]);
    }
    dp[1][0]=1;
    for(int i=2;i<=n ;i++ ){
        ///第i行缩进不超过i-1个单位
        if(prg[i-1]=='f'){
            dp[i][0]=0;
            for(int j=1;j<=i-1 ;j++ ){
                dp[i][j]=dp[i-1][j-1]%MOD;
            }
        }
        else {
            ///从右往左，累计求和
            for(int j=i-2;j>=0 ;j-- ){
                dp[i][j]=(dp[i][j+1]%MOD+dp[i-1][j]%MOD)%MOD;
            }
        }
    }
    int ans=0;
    if(prg[n]=='s')
    for(int i=0;i<=n-1 ;i++ ){
        ans=(ans+dp[n][i])%MOD;
    }
    printf("%d
",ans);
}