#include<cstdio>
#include<cstring>
#include<iostream>
using namespace std;
int n,a,b;
int l[10000];
int dg(int x)
{
if(x==b)return 1;
else
{
if(x+l[x]<b&&x-l[x]>=1)
{
return x+l[x]||x-l[x];
}
if(x-l[x]<1&&x+l[x]<b)
{
return x+l[x];
}
if(x-l[x]>=1&&x+l[x]>b)
{
return x-l[x];
}
else
{
return 9999;
}
}
}
int main()
{
cin>>n>>a>>b;
for(int i=1;i<=n;i++)
{
cin>>l[i];
}
int q=dg(l[a]+1);
if(q==9999)
{
cout<<"-1";
}
else cout<<q+1;
}

深搜都可~
```pascal
program lift;
uses math;
var n,a,b,i,ans,step:longint;
s:array[1..200]of longint;
qwq:array[1..200]of boolean;

procedure dfs(v:longint);
begin
if step>ans then exit;
if v=b then begin ans:=min(step,ans);exit;end;
inc(step);qwq[v]:=false;
if (v-s[v]>=1)and(qwq[v-s[v]]) then
begin
dfs(v-s[v]);
end;
if (v+s[v]<=n)and(qwq[v+s[v]]) then
begin
dfs(v+s[v]);
end;
dec(step);qwq[v]:=true;
end;

begin
readln(n,a,b);
for i:=1 to n do read(s[i]);

ans:=maxlongint;step:=0;
fillchar(qwq,sizeof(qwq),true);
dfs(a);

if ans=maxlongint then writeln(-1)
else writeln(ans);
end.
```

= =

DP，最短路，甚至BFS即可。。。。

var n,i,j,x,y,t,w,p:longint;

q:array[0..4000] of record

dep,pr:longint;

end;

a:array[1..200] of longint;

b:array[1..200] of boolean;

yy:boolean;

begin

assign(input,'LIFT.IN');

assign(output,'LIFT.OUT');

reset(input);rewrite(output);

readln(n,x,y);

for i:=1 to n do read(a[i]);

if x=y then begin writeln(0); close(input);close(output); halt;end;{close~~}

fillchar(b,sizeof(b),true);

b[x]:=true;

q[1].dep:=x;q[1].pr:=0;

t:=1;w:=1;

while t