250pt：
一个学生等老师来上课的，但是他不知道老师啥时候会来的，然后他等waiting时间后觉得无聊就会出去转walking时间，回来等待waiting时间后老师没来就会再次出去。老师会在a...b区间时间任意时刻来，是等概率的。但是老师等t时间后，就会不会让你进来了的。让你求你进不去教室的概率是多少。（所有的数<= 1000W）
思路:因为小于1000w，所以我就暴力把每一分钟的状态都统计出来。
注意长度为0的情况即可（比如老师即到即走的情况）举要特判
#line 7 "LateProfessor.cpp" #include <cstdlib> #include <cctype> #include <cstring> #include <cstdio> #include <cmath> #include <algorithm> #include <vector> #include <string> #include <iostream> #include <sstream> #include <map> #include <set> #include <queue> #include <stack> #include <fstream> #include <numeric> #include <iomanip> #include <bitset> #include <list> #include <stdexcept> #include <functional> #include <utility> #include <ctime> using namespace std; #define PB push_back #define MP make_pair #define REP(i,n) for(i=0;i<(n);++i) #define FOR(i,l,h) for(i=(l);i<=(h);++i) #define FORD(i,h,l) for(i=(h);i>=(l);--i) typedef vector<int> VI; typedef vector<string> VS; typedef vector<double> VD; typedef long long LL; typedef pair<int,int> PII; class LateProfessor { public: double getProbability(int wait, int walk, int late, int st, int end) { double sum = (end - st); int m = wait + walk; double ans = 0; // int last = -1, len = 0; if (st == end){ if (st % m <= wait || (st % m > wait && st % m + late > m)) return 0.0; return 1.0; } for (int i = st; i < end; ++i){ if (i % m < wait || (i % m >= wait && i % m + late >= m)) ++ans; } return 1 - ans / sum; } };
500pt：
给定supersum定义如下
- SuperSum(0 , n) = n, for all positive n.
- SuperSum(k , n) = SuperSum(k-1 , 1) + SuperSum(k-1 , 2) + ... + SuperSum(k-1 , n), for all positive k, n.
给定k,n(k <= 50, n <= 10^9),求supersum（k,n）
思路：乍一看不会做，然后就打了个20*20的表，发现斜着看就是一个杨辉三角，然后直接算可以了
答案就是C(n + k, k + 1)
1 #line 7 "SuperSum.cpp" 2 #include <cstdlib> 3 #include <cctype> 4 #include <cstring> 5 #include <cstdio> 6 #include <cmath> 7 #include <algorithm> 8 #include <vector> 9 #include <string> 10 #include <iostream> 11 #include <sstream> 12 #include <map> 13 #include <set> 14 #include <queue> 15 #include <stack> 16 #include <fstream> 17 #include <numeric> 18 #include <iomanip> 19 #include <bitset> 20 #include <list> 21 #include <stdexcept> 22 #include <functional> 23 #include <utility> 24 #include <ctime> 25 using namespace std; 26 27 #define PB push_back 28 #define MP make_pair 29 30 #define REP(i,n) for(i=0;i<(n);++i) 31 #define FOR(i,l,h) for(i=(l);i<=(h);++i) 32 #define FORD(i,h,l) for(i=(h);i>=(l);--i) 33 #define M 1000000007 34 typedef vector<int> VI; 35 typedef vector<string> VS; 36 typedef vector<double> VD; 37 typedef long long LL; 38 typedef pair<int,int> PII; 39 40 class SuperSum 41 { 42 public: 43 long long power(long long a, long long b){ 44 long long ret = 1; 45 while (b){ 46 if (b&1) ret = (ret * a) % M; 47 b >>= 1; 48 a = (a * a) % M; 49 } 50 return ret; 51 } 52 long long C(int n, int m){ 53 long long ret = 1; 54 for (int i = 1; i <= m; ++i){ 55 ret = (ret * power(i, M - 2)) % M; 56 ret = (ret * (n - i + 1)) % M; 57 } 58 return ret; 59 } 60 int calculate(int K, int N) 61 { 62 int n = K + N; 63 int m = K + 1; 64 return C(n, m); 65 } 66 67 };