#include <bits/stdc++.h>
using namespace std;
const int mx=2000;
const int mod=1000000007;
typedef long long ll;
int n,m;
int st,en;
//(i,x,state);
map<int,int>mp;
ll dp[mx][mx][3];
ll solve(int i,int x,int dir){
if(i==en){
if(x==n){
return 1;}
return 0;
}
// ll &ret=dp[i][x][dir];
// if(ret!=-1){return ret;}
ret=0;
if(dir==0){
for(int j=i+1;j<=n;j++){
if(mp[j]){continue;}
mp[j]=1;
ret=(ret+solve(j,x+1,dir^1))%mod;
mp[j]=0;
}
}else{
for(int j=i-1;j>=1;j--){
if(mp[j]){continue;}
mp[j]=1;
ret=(ret+solve(j,x+1,dir^1))%mod;
mp[j]=0;
}
}return ret%mod;
}
int main() {
cin>>n>>st>>en;
//memset(dp,-1,sizeof(dp));
mp[st]=1;
cout<<(solve(st,1,0)+solve(st,1,1))%mod;
}
Compilation message
kangaroo.cpp: In function 'll solve(int, int, int)':
kangaroo.cpp:19:6: error: 'ret' was not declared in this scope
19 | ret=0;
| ^~~
