2011.cpp

#include <list>

using namespace std;

class State {
public:
    unsigned int current;
    char lastLoop;
    list<char> prevLoops;   //0: ending in +7. 1: ending in /2. 2: ending in *3. 3: ending in -5.
};

int main()  {
    State cur;
    cur.current=2018;
    cur.lastLoop=0;
    list<State> nodes;
    State tmp;
    size_t counter=0;
    for (;;)    {
        if (cur.lastLoop!=0) if (cur.current&1) {
            tmp.current=(cur.current+7)>>1;
            tmp.prevLoops=cur.prevLoops;
            tmp.prevLoops.push_back(1);
            if (tmp.current==2017)  {
                cur=tmp;
                break;
            }
            tmp.lastLoop=1;
            nodes.push_back(tmp);
        }
        if (cur.lastLoop!=1) if (!(cur.current&1))  {
            tmp.current=(cur.current>>1)+7;
            tmp.prevLoops=cur.prevLoops;
            tmp.prevLoops.push_back(0);
            if (tmp.current==2017)  {
                cur=tmp;
                break;
            }
            tmp.lastLoop=0;
            nodes.push_back(tmp);
        }
        if (cur.lastLoop!=2)    {
            tmp.current=(cur.current+(cur.current<<1)-5);
            tmp.prevLoops=cur.prevLoops;
            tmp.prevLoops.push_back(3);
            tmp.lastLoop=3;
            nodes.push_back(tmp);
        }
        if (cur.lastLoop!=3)    {
            tmp.current=cur.current-5;
            tmp.current+=tmp.current<<1;
            tmp.prevLoops=cur.prevLoops;
            tmp.prevLoops.push_back(2);
            if (tmp.current==2017)  {
                cur=tmp;
                break;
            }
            tmp.lastLoop=2;
            nodes.push_back(tmp);
        }
        ++counter;
        cur=nodes.front();
        nodes.pop_front();
    }
    unsigned int n1=2018,n2;
    printf("2011+7=2018.\n");
    list<char>::const_iterator e=cur.prevLoops.end();
    for (list<char>::const_iterator it=cur.prevLoops.begin();it!=e;++it)    {
        switch (*it)    {
            case 0:
                n2=n1>>1;
                printf("%u/2=%u.\n",n1,n2);
                n1=n2;
                n2=n1+7;
                printf("%u+7=%u.\n",n1,n2);
                break;
            case 1:
                n2=n1+7;
                printf("%u+7=%u.\n",n1,n2);
                n1=n2;
                n2=n1>>1;
                printf("%u/2=%u.\n",n1,n2);
                break;
            case 2:
                n2=n1-5;
                printf("%u-5=%u.\n",n1,n2);
                n1=n2;
                n2=n1+(n1<<1);
                printf("%u*3=%u.\n",n1,n2);
                break;
            case 3:
                n2=n1+(n1<<1);
                printf("%u*3=%u.\n",n1,n2);
                n1=n2;
                n2=n1-5;
                printf("%u-5=%u.\n",n1,n2);
                break;
        }
        n1=n2;
    }
    printf("2017-5=2012.\n");
    return 0;
}