【二分答案】爬山

很明显的二分…

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题目

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思路

二分上升用的时间，

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#include<cstdio>
long long m,d,a,b,l,r,ups,downs,uup,ddown;
int main(){
 scanf("%lld%lld%lld%lld",&m,&d,&a,&b);
 --m;
 l = 0; r = m; 
 while(l<r){
  ups = (l+r+1)/2;  //往上用时
  downs = m-ups;  //往下用时
  uup = a+ups*d;  //往上时结束的最高高度
  ddown = b+downs*d;  //往下时开始的高度
  if(uup<ddown) l = ups;  //判断
  if(uup>ddown){
   if(uup-d<=ddown){
    printf("%lld",ddown);
    return 0;
   }
   else r = ups-1;
  }
  if(uup==ddown){
   printf("%lld",uup);
   return 0;
  }
 }
 ups = l;
 downs = m-ups;
 uup = a+ups*d;
 ddown = b+downs*d;
 if(uup>ddown) printf("%lld",ddown);
 else printf("%lld",uup);
}