94分WA#7求调

#include <bits/stdc++.h>
using namespace std;
int t[2009], m[2009];
int n, a, b;
int que[2009];
int qt[2009];
void bfs()
{
    int tail = 1, head = 0;
    t[a] = 1;
    que[1] = a;
    qt[1] = 0;
    do
        {
            head++;
            for(int i = 1; i <= 2; i++)
                {
                    int nx;
                    if(i==1)
                    {
                        nx = que[head]+m[que[head]];
                    }
                    else if(i==2)
                    {
                        nx = que[head]-m[que[head]];
                    }
                    //cout << nx << " ";
                    if(nx<1||nx>n||t[nx]==1) continue;
                    tail++;
                    que[tail] = nx;
                    qt[tail] = qt[head] + 1;
                    t[nx] = 1;
                    if(nx == b)
                    {
                        cout << qt[tail];
                        return;
                    }
                }
        }while(head < tail);
    cout << -1;
}
int main()
{
    cin >> n >> a >> b;
    for(int i = 1; i <= n; i++)
        {
            cin >> m[i];
        }
    bfs();
}