BZ的水题们。。。
这道题的学名叫什么"two pointers"来着。。。就是线性扫过去啊我去、、、
PoPoQQQ称之为"《论排序算法的高效性和合理利用以及能否记得使用排序算法》"2333
1 /************************************************************** 2 Problem: 2348 3 User: rausen 4 Language: C++ 5 Result: Accepted 6 Time:128 ms 7 Memory:1196 kb 8 ****************************************************************/ 9 10 #include <cstdio> 11 #include <algorithm> 12 13 using namespace std; 14 typedef long long ll; 15 typedef double lf; 16 const int N = 100005; 17 const lf eps = 1e-8; 18 19 int n, a[N]; 20 ll ans; 21 22 inline int read() { 23 int x = 0, sgn = 1; 24 char ch = getchar(); 25 while (ch < '0' || '9' < ch) { 26 if (ch == '-') sgn = -1; 27 ch = getchar(); 28 } 29 while ('0' <= ch && ch <= '9') { 30 x = x * 10 + ch - '0'; 31 ch = getchar(); 32 } 33 return sgn * x; 34 } 35 36 int main() { 37 int i, j; 38 n = read(); 39 for (i = 1; i <= n; ++i) 40 a[i] = read(); 41 sort(a + 1, a + n + 1); 42 for (i = j = 1; i <= n; ++i) { 43 while (a[j] + eps < (lf) a[i] * 0.9) 44 ++j; 45 ans += i - j; 46 } 47 printf("%lld ", ans); 48 return 0; 49 }