【题解】001:特殊密码锁

http://cxsjsxmooc.openjudge.cn/2018t2winterw1/001/

提示：找出枚举类题目的局部是什么，以小见大求全部，从而避免枚举大量情况

观察：前i个可以推出第i+1个的情况

启示：关注问题本身的解决方案和实现过程，并非案例给的情形拼凑

#include<memory>
#include<string>
#include<cstring>
#include<cstdio>
#include<iostream>
using namespace std;
char a[40],b[40];
int now=0,change=0,goal=0;
int len;
int ans=40,sumnow=0;

int GetBit(int num, int i)
{
return (num >> i) & 1;
}

int SetBit(int i, int v)
{
   int sum=0;
   if(v) sum |= (1 << (i));
   else sum &= ~(1 << (i));
   return sum;
}

void FlipBit(int &change, int i)
{
change ^= (1 << i);
}

void ClickBit(int &change, int i)
{
   if(i>=0&&i<=len-1)
   {
       sumnow++;
       if(i==0)
       {
           FlipBit(change, i);
           FlipBit(change, i+1);
       //   printf("改变1：i=%d,i+1=%d\n",i,i+1);
       }
       else if(i==len-1)
       {
           FlipBit(change, i);
           FlipBit(change, i-1);
       //   printf("改变2：i=%d,i-1=%d\n",i,i-1);
       }
       else
       {
           FlipBit(change, i);
           FlipBit(change, i-1);
           FlipBit(change, i+1);
       //   printf("改变3：i-1=%d,i=%d,i+1=%d\n",i-1,i,i+1);
       }
   }
}
/*bool CmpBit(int &change, int &goal, int i)
{
   printf("此时的第%d位change=%d,goal=%d\n",i,change,goal);
   if(GetBit(change,i) == GetBit(goal,i)) return 1;
   else return 0;
}*/
void Ans(int v)
{
   sumnow = 0;
   change = now;
   //printf("开始：change=%d\n",change);
   if(v)
   {
       ClickBit(change, 0);
   }
   for(int j=0;j<len;++j)
   {
       //printf("v=%d：j=%d,change=%d,goal=%d,sumnow=%d\n",v,j,change,goal,sumnow);//
       //printf("change第%d位=%d,goal第%d位=%d\n",j,GetBit(change,j),j,GetBit(goal,j));
       if(GetBit(change,j) == GetBit(goal,j))
       {
           if(change == goal)
           {
               if(sumnow < ans) {ans = sumnow;}// printf("按下：j=%d,ans=%d\n",j,ans);
               else break;
           }
           continue;
       }
       else
       {
           if(j!=len-1)ClickBit(change,j+1);
           //printf("change=%d\n",change);
           continue;
       }
   }
}
int main()
{
   int i,j;
   gets(a);
   gets(b);
   len = strlen(a);
   //printf("a=%s,b=%s,goal=%d\n",a,b,goal);
   for(i=0;i<len;++i)
   {
       if(a[i]=='0') now += SetBit(i,0);
       if(a[i]=='1') now += SetBit(i,1);
       if(b[i]=='0') goal += SetBit(i,0);
       if(b[i]=='1') goal += SetBit(i,1);
       //printf("i=%d,a[%d]=%c,now=%d,b[%d]=%c,goal=%d\n",i,i,a[i],now,i,b[i],goal);//
   }
   //printf("now=%d,goal=%d\n",now,goal);//
   //第0个开关按下
   Ans(1);
   //第0个开关不按
   Ans(0);
   //没答案
   if(ans == 40) printf("impossible");
   else printf("%d",ans);
   return 0;
}

【题解】001:特殊密码锁

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