hdu 1548 A strange lift

SPFA

#include<stdio.h>
#include<string.h>
#include<math.h>
#include<vector>
#include<algorithm>
using namespace std;
const int maxn = 222;
int k[maxn], ji[maxn];
vector<int> abc[maxn];
struct aaa{int node, tot;}dt[maxn*maxn];
bool cmp(const aaa&a, const aaa&b){return a.tot < b.tot;}
int main()
{
    int N, A, B, i, j;
    while (~scanf("%d", &N))
    {
        if (N == 0) break;
        scanf("%d%d", &A, &B);
        for (i = 0; i < maxn; i++) ji[i] = 999999999, abc[i].clear();
        for (i = 1; i <= N; i++) scanf("%d", &k[i]);
        for (i = 1; i <= N; i++)
        {
            if (i + k[i] <= N) abc[i].push_back(i + k[i]);
            if (i - k[i] >= 1)abc[i].push_back(i - k[i]);
        }
        ji[A] = 0;dt[0].node = A;dt[0].tot = 0;int b = 0;
        for (i = 0; i <= b; i++)
        {
         for (j = 0; j < abc[dt[i].node].size(); j++)
            {

                if (dt[i].tot + 1 < ji[abc[dt[i].node][j]])
                {
                    b++;
                    dt[b].node = abc[dt[i].node][j];
                    dt[b].tot = dt[i].tot + 1;
                    ji[abc[dt[i].node][j]] = dt[i].tot + 1;
                }
            }
        }
        if (ji[B] != 999999999)printf("%d\n", ji[B]);
        else printf("-1\n");
    }
    return 0;
}