將本題作為bfs模板

#include <bits/stdc++.h>

#define     INF     0x3f3f3f3f

using namespace std;

const int maxn = 305;

int n, a, b;

typedef struct node
{
    int f;
    int s;
    node(int ff, int ss) {
        f = ff;
        s = ss;
    }
}node;


int arr[maxn];
bool vis[maxn];
queue<node> q;
int ans;

void init()
{
    ans = 0;
    memset(vis, false, sizeof(vis));
    while (!q.empty()) q.pop();
}

void bfs()
{
    q.push(node(a, 0));
    vis[a] = true;

    while (!q.empty()) {

        node x = q.front();

        q.pop();

        if (x.f == b) {
            ans = x.s;
            return ;
        }

        int xx;

        xx = x.f + arr[x.f];
        if (!vis[xx] && xx > 0 && xx <= n) {
            vis[xx] = true;
            q.push(node(xx, x.s + 1));
        }

        xx = x.f - arr[x.f];
        if (!vis[xx] && xx > 0 && xx <= n) {
            vis[xx] = true;
            q.push(node(xx, x.s + 1));
        }
    }

}


int main()
{
    while (scanf("%d", &n) != EOF && n) {

        scanf("%d%d", &a, &b);

        for (int i = 1; i <= n; i++) scanf("%d", &arr[i]);

        init();

        if (a == b) printf("0\n");
        else {
            bfs();
            if (ans) printf("%d\n", ans);
            else printf("-1\n");
        }

    }
    return 0;
}