湖南大学ACM程序设计新生杯大赛(同步赛)A-Array 【证明+暴力】
2017-12-24 18:31
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时间限制:C/C++ 1秒,其他语言2秒
空间限制:C/C++ 131072K,其他语言262144K
64bit IO Format: %lld
题目描述
Given an array A with length n a[1],a[2],…,a
where a[i] (1<=i<=n) is positive integer.
Count the number of pair (l,r) such that a[l],a[l+1],…,a[r] can be rearranged to form a geometric sequence.
Geometric sequence is an array where each term after the first is found by multiplying the previous one by a fixed, non-zero number called the common ratio. i.e. A = [1,2,4,8,16] is a geometric sequence.
输入描述:
The first line is an integer n (1 <= n <= 100000).
The second line consists of n integer a[1],a[2],…,a
where a[i] <= 100000 for 1<=i<=n.
输出描述:
An integer answer for the problem.
示例1
输入
5
1 1 2 4 1
输出
11
说明
The 11 pairs of (l,r) are (1,1),(1,2),(2,2),(2,3),(2,4),(3,3),(3,4),(3,5),(4,4),(4,5),(5,5).
示例2
输入
10
3 1 1 1 5 2 2 5 3 3
输出
20
备注:
The answer can be quite large that you may use long long in C++ or the similar in other languages.
题意:让你找出所有的等比序列。
分析:逆向思维便可以优雅的暴力。由于数据是小于十万的,公比为2的序列长度最长为17,所以我们可以枚举序列长度。
公比不能为小数吗?当然可以,但是如果是小数的话,可以转化成分数,那么必须是分母的整数幂。然而分母最小是2,所以证毕!
注意:比赛的时候被精度卡住,卡在90%的数据上过不了。以后能用long long int解决的绝不用double。
空间限制:C/C++ 131072K,其他语言262144K
64bit IO Format: %lld
题目描述
Given an array A with length n a[1],a[2],…,a
where a[i] (1<=i<=n) is positive integer.
Count the number of pair (l,r) such that a[l],a[l+1],…,a[r] can be rearranged to form a geometric sequence.
Geometric sequence is an array where each term after the first is found by multiplying the previous one by a fixed, non-zero number called the common ratio. i.e. A = [1,2,4,8,16] is a geometric sequence.
输入描述:
The first line is an integer n (1 <= n <= 100000).
The second line consists of n integer a[1],a[2],…,a
where a[i] <= 100000 for 1<=i<=n.
输出描述:
An integer answer for the problem.
示例1
输入
5
1 1 2 4 1
输出
11
说明
The 11 pairs of (l,r) are (1,1),(1,2),(2,2),(2,3),(2,4),(3,3),(3,4),(3,5),(4,4),(4,5),(5,5).
示例2
输入
10
3 1 1 1 5 2 2 5 3 3
输出
20
备注:
The answer can be quite large that you may use long long in C++ or the similar in other languages.
题意:让你找出所有的等比序列。
分析:逆向思维便可以优雅的暴力。由于数据是小于十万的,公比为2的序列长度最长为17,所以我们可以枚举序列长度。
公比不能为小数吗?当然可以,但是如果是小数的话,可以转化成分数,那么必须是分母的整数幂。然而分母最小是2,所以证毕!
注意:比赛的时候被精度卡住,卡在90%的数据上过不了。以后能用long long int解决的绝不用double。
#include<iostream> #include<cstring> #include<cstdio> #include<algorithm> using namespace std; #define ll long long int const double eps = 1e-8; const int maxn = 1e5 + 10; double a[maxn]; double b[maxn]; int main() { int n; scanf("%d", &n); for (int i = 1; i <= n; i++) { scanf("%lf", &a[i]); b[i] = a[i]; } ll ans = 2*n-1; for (int i = 1; i <= n; i++) { for (int j = 1; j <= 17; j++) { if (i + j - 1 > n) break; if (j == 1 || j == 2) { continue; } sort(a + i, a + i + j); double cs = a[i + 1] / a[i]; int flag = 1; for (int k = i + 1; k <= i + j - 1; k++) { double ct = a[k] / a[k - 1]; if (fabs(ct - cs) > eps) { flag = 0; break; } } if (fabs(cs - 1) < eps) flag = 0; ans += 1ll * flag; //cout << flag << endl; for (int k = i; k <= i + j - 1; k++) { a[k] = b[k]; } } } ll sum = 1; for (int i = 2; i <= n; i++) { if (a[i] == a[i - 1]) sum++; else sum = 1; if(sum>=3) ans = ans + sum - 2; } printf("%lld\n", ans); return 0; }
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