poj 3278 cow （bfs）

来源：互联网发布：linux查看用户文件编辑：程序博客网时间：2024/06/14 13:18

写法一：模拟队列

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

using namespace std;

const int N = 700500;
const int inf = 0x3f3f3f3f;

struct mark{
int x;
int k;
};

mark a[N];
int book[N];

int main()
{
int n, m;

while(scanf("%d %d", &n, &m)!=EOF)
{
if(n>m)
printf("%d\n", n-m);//加上这步可以大大优化，减少时间
else
{
int head = 0, tail=1;
a[0].x = n;
a[0].k = 0;
memset(book, 0 ,sizeof(book));
book[n] = 1;
while(head<tail)
{
if(a[head].x==m)
{
printf("%d", a[head].k);
break;
}
if(!book[a[head].x+1]&&a[head].x+1<=m)
{
a[tail].x = a[head].x+1;
book[a[head].x+1] = 1;
a[tail++].k=a[head].k+1;
}
if(!book[a[head].x-1]&&a[head].x-1>=0)
{
a[tail].x = a[head].x-1;
book[a[head].x-1] = 1;
a[tail++].k=a[head].k+1;
}
if(!book[a[head].x*2]&&a[head].x*2<=2*m)
{
a[tail].x = a[head].x*2;
book[a[head].x*2] = 1;
a[tail++].k=a[head].k+1;
}
head++;
}
}
}
return 0;
}

写法二：STL队列

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

using namespace std;

const int N = 200500;
const int inf = 0x3f3f3f3f;
bool book[N];
int step[N];

int main()
{
int n, m;

while(scanf("%d %d", &n, &m)!=EOF)
{
if(n>m)
printf("%d\n", n-m);//stl必须得有这步。
else
{
memset(book, false ,sizeof(book));
memset(step, 0 ,sizeof(step));
int head, next, flag = 0;
queue<int>q;
q.push(n);
book[n] = true;
step[n] = 0;

while(!q.empty())
{
head = q.front();
q.pop();
for(int i = 0; i<3; i++)
{
if(i==0)
next = head - 1;
else if(i==1)
next = head + 1;
else
next = head * 2;

if(next>=2*m||next<0)
continue;
if(!book[next])
{
q.push(next);
step[next] = step[head] + 1;
book[next] = 1;
}
if(next==m)
{
printf("%d\n", step[next]);
flag = 1;
break;
}
}
if(flag == 1)
break;
}
}
}
return 0;
}

0 0