~~我太菜了，所以只能打个BFS给你~~
```
#include<bits/stdc++.h>
using namespace std;
bool p[200005];
// 起始 终止
int newx, n, s, t, a[200005];
struct dian{
int ans, temp;
};
bool check(int x){
return x <= n && x > 0 && !p[x];
}
int bfs(int x){
queue <dian> q;
dian f;
p[x] = true;
q.push({x, 0});
while(!q.empty()){
f = q.front(), q.pop();
if(f.ans == t) return f.temp;
// printf("%d %d\n", f.temp, f.ans);
if(check(f.ans + a[f.ans])) q.push({f.ans + a[f.ans], f.temp + 1}), p[f.ans + a[f.ans]] = true;
if(check(f.ans - a[f.ans])) q.push({f.ans - a[f.ans], f.temp + 1}), p[f.ans - a[f.ans]] = true;
}
return -1;
}
int main(){
scanf("%d %d %d", &n, &s, &t);
for(int i = 1;i <= n;i ++) scanf("%d", &a[i]);
printf("%d", bfs(s));
return 0;
}
```
by dzsf_lhz @ 2024-03-16 08:15:51