1011: [HNOI2008]遥远的行星
Time Limit: 10 Sec Memory Limit: 162 MBSec Special JudgeSubmit: 4974 Solved: 1864
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Description
直线上N颗行星,X=i处有行星i,行星J受到行星I的作用力,当且仅当i<=AJ.此时J受到作用力的大小为 Fi->j=
Mi*Mj/(j-i) 其中A为很小的常量,故直观上说每颗行星都只受到距离遥远的行星的作用。请计算每颗行星的受力
,只要结果的相对误差不超过5%即可.
Input
第一行两个整数N和A. 1<=N<=10^5.0.01< a < =0.35,接下来N行输入N个行星的质量Mi,保证0<=Mi<=10^7
Output
N行,依次输出各行星的受力情况
Sample Input
5 0.3
3
5
6
2
4
3
5
6
2
4
Sample Output
0.000000
0.000000
0.000000
1.968750
2.976000
0.000000
0.000000
1.968750
2.976000
HINT
精确结果应该为0 0 0 2 3,但样例输出的结果误差不超过5%,也算对
析:因为这个题误差不超过 5%,所以对于小数据我们就可以直接进行暴力,然后大数据我们就可以进行误差分析,A * j 得到一个数 t,我们就可以用 j - t / 2来代替所有的分母,这样的话就可以用前缀进行优化了,时间复杂度就小了,但是要注意这个题的是卡精度的,在求 t 的时候要加上一个eps,来控制精度。
代码如下:
#pragma comment(linker, "/STACK:1024000000,1024000000") #include <cstdio> #include <string> #include <cstdlib> #include <cmath> #include <iostream> #include <cstring> #include <set> #include <queue> #include <algorithm> #include <vector> #include <map> #include <cctype> #include <cmath> #include <stack> #include <sstream> #include <list> #include <assert.h> #include <bitset> #include <numeric> #define debug() puts("++++") #define gcd(a, b) __gcd(a, b) #define lson l,m,rt<<1 #define rson m+1,r,rt<<1|1 #define fi first #define se second #define pb push_back #define sqr(x) ((x)*(x)) #define ms(a,b) memset(a, b, sizeof a) #define sz size() #define pu push_up #define pd push_down #define cl clear() #define all 1,n,1 #define FOR(i,x,n) for(int i = (x); i < (n); ++i) #define freopenr freopen("in.txt", "r", stdin) #define freopenw freopen("out.txt", "w", stdout) using namespace std; typedef long long LL; typedef unsigned long long ULL; typedef pair<int, int> P; const int INF = 0x3f3f3f3f; const LL LNF = 1e17; const double inf = 1e20; const double PI = acos(-1.0); const double eps = 1e-6; const int maxn = 1e5 + 10; const int maxm = 3e5 + 10; const int mod = 100003; const int dr[] = {-1, 0, 1, 0}; const int dc[] = {0, -1, 0, 1}; const char *de[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"}; int n, m; const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31}; inline bool is_in(int r, int c) { return r >= 0 && r < n && c >= 0 && c < m; } double sum[maxn]; double b[maxn]; int main(){ double a; scanf("%d %lf", &n, &a); for(int i = 1; i <= n; ++i){ scanf("%lf", b + i); sum[i] = sum[i-1] + b[i]; double ans = 0.; int t = i * a + eps; if(i > 100){ double xx = i - i * a / 2.; ans = sum[t] * 1. * b[i] / xx; } else { for(int j = 1; j <= t; ++j) ans += b[i] * 1. * b[j] / (i - j); } printf("%.6f\n", ans); } return 0; }