HDU 1548 A strange lift

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题目地址：点击打开链接

思路：单向图，有不可能的情况，用BFS做也可以

AC代码：

#include<iostream>#include<cstring>#define MAX1 400000using namespace std;int map[210][210],visit[210],dist[210];int n,a,b;void dijkstra(){    int i,j,min,k;    for(i=1; i<=n; i++)    {        dist[i] = map[a][i];        visit[i] = 0;    }    dist[a] = 0;    visit[a] = 1;    for(i=1; i<n; i++)    {        min = MAX1;        for(j=1; j<=n; j++)        {            if(visit[j] == 0 && dist[j] < min)            {                min = dist[j];                k = j;            }        }        if(min == MAX1)            return;        visit[k] = 1;        for(j=1; j<=n ;j++)        {            if(visit[j] == 0 && dist[k] + map[k][j] < dist[j])                dist[j] = dist[k] + map[k][j];        }    }}int main(){    int i,j,x;    while(cin>>n && n)    {        cin>>a>>b;        for(i=1; i<=n; i++)        {            for(j=1; j<=n; j++)            {                map[i][j] = MAX1;            }        }        for(i=1; i<=n; i++)        {            cin>>x;            if(i+x<=n)                map[i][i+x] = 1;            if(i-x>=1)                map[i][i-x] = 1;        }        dijkstra();//注意语句cout<<(dist[b] == MAX1 ? -1 : dist[b])        if(dist[b]  == MAX1)            cout<<"-1"<<endl;        else            cout<<dist[b]<<endl;    }    return 0;}

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