HDU 1548 A strange lift （Dijkstra）

https://vjudge.net/problem/HDU-1548

题意：

电梯每层有一个不同的数字，例如第n层有个数字k，那么这一层只能上k层或下k层，但是不能低于一层或高于n层，给定起点与终点，要求出最少要按几次键。

思路：

可以用BFS，也可以用迪杰斯特拉算法。

#include<iostream> 
#include<cstring>
#include<algorithm>
#include<vector>
using namespace std;

#define INF 100000000

int n, A, B;
int map[205][205];
int vis[205];
int d[205];
int num[205];

void Dijkstra()
{
    memset(vis, 0, sizeof(vis));
    for (int i = 1; i <= n; i++)
    {
        num[i] = map[A][i];
    }
    num[A] = 0;
    vis[A] = 1;
    for (int i = 1; i < n; i++)
    {
        int min = INF;
        int pos;
        for (int j = 1; j <= n; j++)
        {
            if (num[j] < min && !vis[j])
            {
                pos = j;
                min = num[j];
            }
        }
        if (min == INF)    break;
        vis[pos] = 1;
        for (int j = 1; j <= n; j++)
        {
            if (num[pos] + map[pos][j] < num[j] && !vis[j])
                num[j] = num[pos] + map[pos][j];
        }
    }
    if (num[B] == INF)  printf("-1
");
    else printf("%d
", num[B]);
}

int main()
{
    //freopen("D:\txt.txt", "r", stdin);
    int a;
    while (scanf("%d", &n) && n)
    {
        scanf("%d%d", &A, &B);
        for (int i = 1; i <= n; i++)
        for (int j = 1; j <= n; j++)
            map[i][j] = INF;
        for (int i = 1; i <= n; i++)
        {
            scanf("%d", &a);
            if (i + a <= n)
                map[i][i + a] = 1;
            if (i - a >= 0)
                map[i][i - a] = 1; 
        }
        Dijkstra();
    }
    return 0;
}