有点懵比~~

没看懂题解说的随机数概率什么的=_=

 

先贴上dalao代码

 

1 #include 
      
        2  3 using namespace std; 4  5 inline pair 
       
         ask(int id) { 6   printf("? %d\n", id); 7   fflush(stdout); 8   pair 
        
          p; 9   scanf("%d %d", &p.first, &p.second);10   return p;11 }12 13 inline void finish(int value) {14   printf("! %d\n", value);15   fflush(stdout);16   exit(0);17 }18 19 inline int RAND(int n) {20   return abs((rand() << 15) + rand()) % n;21 }22 23 const int MAGIC = 1000;24 25 int main() {26   int n, start, x;27   scanf("%d %d %d", &n, &start, &x);28   srand(time(0));29   set 
         
           all;30   all.insert(start);31   while ((int) all.size() < min(n, MAGIC)) {32     all.insert(RAND(n) + 1);33   }34   vector < pair 
          
            > v;35   for (int i : all) {36     pair 
           
             z = ask(i);37 v.emplace_back(z.first, i);38 }39 sort(v.begin(), v.end());40 int ptr = start;41 for (int i = 0; i < (int) v.size(); i++) {42 if (v[i].first < x) {43 ptr = v[i].second;44 }45 }46 while (ptr != -1) {47 pair 
            
              z = ask(ptr);48 if (z.first >= x) {49 finish(z.first);50 return 0;51 }52 ptr = z.second;53 }54 finish(-1);55 return 0;56 }