python/TangDou/Bfs/3_QiGuaiDianTi.cpp

#include <bits/stdc++.h>

using namespace std;
const int N = 100010;
typedef pair<int,int> PII;
int n;
int a, b;
int k[N];
int st[N];
queue<PII> q;
int step = -1;

void bfs() {
    //初始化队列
    q.push({a, 0});
    st[a] = 1;
    while (q.size()) {
        auto t = q.front();
        q.pop();
        if (t.first == b) {
            step = t.second;
            break;
        }
        int x = t.first + k[t.first];
        if (x <= n && !st[x]) {
            q.push({x, t.second + 1});
            st[x] = 1;
        }
        x = t.first - k[t.first];
        if (x >= 1 && !st[x]) {
            q.push({x, t.second + 1});
            st[x] = 1;
        }
    }
}
int main() {
    //n是几层楼，a:从几层出发 ,b:到几层去
    cin >> n >> a >> b;
    for (int i = 1; i <= n; i++) cin >> k[i]; //记录每层楼的可以按下的数字
    bfs();
    printf("%d", step);
    return 0;
}