标签：enc 不难 数列 soft class etc font table eve
| Time Limit: 1000MS | Memory Limit: 65536K | |
| Total Submissions: 8371 | Accepted: 2911 |
Description
Given N numbers, X1, X2, ... , XN, let us calculate the difference of every pair of numbers: ∣Xi - Xj∣ (1 ≤ i ＜ j ≤ N). We can get C(N,2) differences through this work, and now your task is to find the median of the differences as quickly as you can!
Note in this problem, the median is defined as the (m/2)-th smallest number if m,the amount of the differences, is even. For example, you have to find the third smallest one in the case of m = 6.
Input
The input consists of several test cases.
In each test case, N will be given in the first line. Then N numbers are given, representing X1, X2, ... , XN, ( Xi ≤ 1,000,000,000 3 ≤ N ≤ 1,00,000 )
Output
For each test case, output the median in a separate line.
Sample Input
4 1 3 2 4 3 1 10 2
Sample Output
1 8
Source
1 #include <iostream> 2 #include <cstdio> 3 #include <cstdlib> 4 #include <cstring> 5 #include <algorithm> 6 #define max(a, b) ((a) > (b) ? (a) : (b)) 7 #define min(a, b) ((a) < (b) ? (a) : (b)) 8 9 inline void read(long long &x) 10 { 11 x = 0;char ch = getchar(), c = ch; 12 while(ch < ‘0‘ || ch > ‘9‘)c = ch, ch = getchar(); 13 while(ch <= ‘9‘ && ch >= ‘0‘)x = x * 10 + ch - ‘0‘, ch = getchar(); 14 if(c == ‘-‘)x = -x; 15 } 16 17 const long long MAXN = 100000 + 10; 18 19 long long n,num[MAXN]; 20 21 long long check(long long ans) 22 { 23 long long tot = 0; 24 long long r = 2; 25 for(register long long l = 1;l <= n;++ l) 26 { 27 while(num[r] - num[l] <= ans && r <= n)++ r; 28 tot += r - l - 1; 29 } 30 if(tot >= (n * (n - 1)/2 + 1)/2 )return 1; 31 else return 0; 32 } 33 34 int main() 35 { 36 while(scanf("%lld", &n) != EOF) 37 { 38 long long ma = -1; 39 for(register long long i = 1;i <= n;++ i) read(num[i]), ma = max(ma, num[i]); 40 std::sort(num + 1, num + 1 + n); 41 long long l = 1, r = ma, ans = 0; 42 while(l <= r) 43 { 44 long long mid = (l + r) >> 1; 45 if(check(mid))ans = mid, r = mid - 1; 46 else l = mid + 1; 47 } 48 printf("%lld\n", ans); 49 } 50 return 0; 51 }
标签：enc 不难 数列 soft class etc font table eve
原文地址：http://www.cnblogs.com/huibixiaoxing/p/7641844.html
