61 lines
1.3 KiB
C++
61 lines
1.3 KiB
C++
#include<cstdio>
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#include<iostream>
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#include<cstring>
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#include<cmath>
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#include<queue>
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#define maxn 200 + 10
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bool vis[maxn];
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int n, a, b,dis[maxn];
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using namespace std;
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struct node
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{
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int now;
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int step;
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};
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int bfs(int aa, int bb)
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{
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queue<node>q;
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vis[aa] = 1;
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node start,next;
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start.now = aa;
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start.step = 0;
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q.push(start);
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while (!q.empty())
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{
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node s = q.front();
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q.pop();
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if (s.now == b)
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{
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return s.step;
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}
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for (int i = 0; i < 2; i++)
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{
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if(i==0)
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next.now = s.now+dis[s.now];
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else
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next.now = s.now-dis[s.now];
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if(!vis[next.now]&&next.now>=1&&next.now<=n)
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{
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if(next.now==b)
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return s.step+1;
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vis[next.now] = 1;
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next.step = s.step+1;
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q.push(next);
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}
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}
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}
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return -1;
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}
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int main() {
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while (scanf("%d", &n) != EOF && n)
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{
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memset(vis, 0, sizeof(vis));
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cin >> a >> b;
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for(int i = 1;i<=n;i++)
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cin>>dis[i];
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int ans = bfs(a, 0);
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cout<<ans<<endl;
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}
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return 0;
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}
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