一开始以为死于精度……调了半天发现死于long long……
一、二分法:
#include<cstdio> #include<cstring> #include<algorithm> using namespace std; bool cmp(const int &a,const int &b){return a>b;} int n,a[100001],b[100001]; long long ans; int main() { scanf("%d",&n); for(int i=1;i<=n;++i) scanf("%d",&a[i]); sort(a+1,a+n+1,cmp); memcpy(b,a,(n+1)*sizeof(int)); for(int i=1;i<=n;++i) b[i]*=10; for(int i=1;i<=n;++i) ans+=(long long)(upper_bound(b+i+1,b+n+1,a[i]*9,cmp)-b-i-1); printf("%lld ",ans); return 0; }
二、尺取法:
#include<cstdio> #include<algorithm> using namespace std; bool cmp(const int &a,const int &b){return a>b;} int n,a[100001]; long long ans; int main() { scanf("%d",&n); for(int i=1;i<=n;++i) scanf("%d",&a[i]); sort(a+1,a+n+1,cmp); int head=1,tail=1; while(1) { while(a[tail]*10>=a[head]*9 && tail<=n) ++tail; if(head==n) break; ans+=(long long)(tail-head-1); ++head; } printf("%lld ",ans); return 0; }