题解 | 奇怪的电梯

原题链接A8051 奇怪的电梯
bfs板子，用bfs层级遍历，求最短路

#include <bits/stdc++.h>
using namespace std;
int n,a,b,k[300];
bool vis[300];
int dx[] = {1,-1};
//记录走过的点
struct node{
    int x;
    int step;
};
//bfs模版
int bfs(int sx,int ex){
    //标记首点
    queue<node> q;
    q.push({sx,0});
    vis[sx] = 1;
    //层级遍历
    while(!q.empty()){
        node now = q.front();
        q.pop();
        if(now.x == ex) return now.step;
        for(int i = 0;i < 2;i ++){
            int nx = now.x + k[now.x] * dx[i];
            if(nx < 1 || nx > n) continue;
            if(vis[nx]) continue;
            vis[nx]= 1;
            q.push({nx,now.step+1});
        }
    }
    //失败
    return -1;
}
int main(){
    cin >> n >> a >> b;
    for(int i = 1;i <= n;i ++)
        cin >> k[i];
    cout << bfs(a,b);
}