总时间限制:

2000ms

内存限制:

65536kB

描述

农夫知道一头牛的位置，想要抓住它。农夫和牛都位于数轴上，农夫起始位于点N(0<=N<=100000)，牛位于点K(0<=K<=100000)。农夫有两种移动方式：

1、从X移动到X-1或X+1，每次移动花费一分钟

2、从X移动到2*X，每次移动花费一分钟

 

假设牛没有意识到农夫的行动，站在原地不动。农夫最少要花多少时间才能抓住牛？

 

输入

两个整数，N和K

输出

一个整数，农夫抓到牛所要花费的最小分钟数

样例输入

5 17

样例输出

4
深搜 炸：

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cstring>

using namespace std;
const int N=100010;

bool vis[N];
int people;
int milk;
int answer=99999999;
int nowans=0;

inline int read()
{
    int x=0;char c=getchar();
    while(c<‘0‘||c>‘9‘)c=getchar();
    while(c>=‘0‘&&c<=‘9‘)x=x*10+c-‘0‘,c=getchar();
    return x;
}

void dfs(int nowpeople)
{
    vis[nowpeople]=1;
    if(nowpeople==milk)
    {
        answer=min(answer,nowans);
        return ;
    }
    if(!vis[nowpeople+1]&&nowpeople+1>0&&nowpeople+1<=milk+1)
    {
        nowans++;
        vis[nowpeople+1]=1;
        dfs(nowpeople+1);
        nowans--;
        vis[nowpeople+1]=0;
    }
    if(!vis[nowpeople-1]&&nowpeople-1>0&&nowpeople-1<=milk+1)
    {
        nowans++;
        vis[nowpeople-1]=1;
        dfs(nowpeople-1);
        nowans--;
        vis[nowpeople-1]=0;
    }
    if(!vis[nowpeople*2]&&nowpeople*2>0&&nowpeople*2<=milk+1)
    {
        nowans++;
        vis[nowpeople*2]=1;
        dfs(nowpeople*2);
        nowans--;
        vis[nowpeople*2]=0;
    }
}

int main()
{
    people=read();
    milk=read();
    dfs(people);
    printf("%d",answer);
    return 0;
} 

广搜：

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<queue>
#include<cstdlib>

using namespace std;
const int N=100010;

struct node{
    int x,step;
}now,nxt,top;
int peo,milk;
bool vis[N];
queue<node>q;

inline int read()
{
    int x=0;char c=getchar();
    while(c<‘0‘||c>‘9‘)c=getchar();
    while(c>=‘0‘&&c<=‘9‘)x=x*10+c-‘0‘,c=getchar();
    return x;
}

inline void bfs(int start)
{
    now.x=start;
    now.step=0;
    q.push(now);
    while(!q.empty())
    {
        top=q.front();
        q.pop();
        int x=top.x;
        if(x==milk)
        {
            printf("%d\n",top.step);
            exit(0);
        }
        if(x+1>0&&x+1<=milk+1&&!vis[x+1])
        {
            vis[x+1]=1;
            nxt.x=x+1;
            nxt.step=top.step+1;
            q.push(nxt);
        }
        if(x-1>=0&&x-1<=milk+1&&!vis[x-1])
        {
            vis[x-1]=1;
            nxt.x=x-1;
            nxt.step=top.step+1;
            q.push(nxt);
        }
        if(x*2>=0&&x*2<=milk+1&&!vis[x*2])
        {
            vis[x*2]=1;
            nxt.x=x*2;
            nxt.step=top.step+1;
            q.push(nxt);
        }
    }
}

int main()
{
    peo=read();
    milk=read();
    bfs(peo);
    return 0;
}

简单：

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>

using namespace std;

int a[100001],b[100001],c[100001];

int tot=0;

int print(int d) 
{
    if(c[d]!=0) print(c[d]);
    tot++;
}
int main() 
{
    memset(b,0,sizeof(b));
    memset(a,0,sizeof(a));
    int n,k,x;
    cin>>n>>k;
    if(n==k) 
    {
        cout<<0<<endl;
        return 0;
    }

    a[1]=n;
    b[n]=1;
    int head=0,tail=1;

    while(head!=tail) 
    {
        head++;
        for(int i=1; i<=3; ++i) 
        {
            if(i==1) x=a[head]+1;
            if(i==2) x=a[head]-1;
            if(i==3) x=a[head]*2;
            if(x>=0&&b[x]==0&&x<=100000) 
            {
                tail++;
                a[tail]=x;
                c[tail]=head;
                if(x==k) 
                {
                    print(tail);
                    cout<<tot-1<<endl;
                    head=tail;
                    break;
                }
                b[x]=1;
            }
        }
    }
}

 

2971:抓住那头牛